According to me, there are three major considerations when choosing where/how to convert. These three guideposts should help you decide a) the movement you want to convert with and then b) the community/rabbi/beit din you want to convert with.
a) How you feel about your conversion.
At the end of the day, this should be the most important: Do you feel that you are fully and legally Jewish? Usually, converts shift this to the backseat in favor of the other two concerns. But if you don't take this seriously and convert in a movement/community you're not comfortable with, it will tear at you because your internal and external selves will be out of alignment.
This is where people start talking about money, jobs, and family impeding a "healthier" choice. Of all things, your relationship with G-d should be the foundation for those things. However, people fear change, and conversion can bring change you never even imagined. And sometimes, you really are between a rock and a hard place. Think creatively and you may find a solution that is even better than your current situation! Flexibility, a sense of adventure, and a healthy dose of patience will serve you well in all aspects of your conversion. I also recommend having creative and trustworthy people to brainstorm with!
Don't sell this point short. It'll make you unhappy if you do.
b) How the community feels about your conversion.
In theory, whatever community you're converting in should accept the conversion their leader does. The problem usually comes when you move or when you're dealing with the "larger" Jewish community, even if it's the Jewish day school down the street. This is the element most out of your control.
Really, this is the one that takes patience and a thick skin. Try not to wear your heart on your sleeve. Your conversion is what it is, and no amount of cajoling from you will make it acceptable to someone who doesn't want to accept it. Nine times out of ten, it's better to just walk away and try to accomplish your goal somewhere else. Hopefully, you have that option! Sometimes you don't. And if you don't, is there a way to create a similar opportunity yourself or within your own community? You may have located a real need for your community!
Once you've thought about these things, you can decide where you want to live. That may or may not be where you currently live, and if you're planning to convert orthodox, you shouldn't make that final decision until you've spoken to a conversion beit din about your situation. After all, one of the worst conversion issues to have is being required to move to a new community, but your situation delays or prohibits that move. On the other hand, if you're planning to move to New York City, Los Angeles, or Toronto, you can be pretty certain that they could only ask you to move to a different part of town. I don't recommend buying a house anywhere until your conversion is finished, simply to avoid these issues. And if you already own a home, realize that you may be asked to sell it and move, and that may be a condition of your conversion process.
This factor is also where you should assess which beit din within a movement you want to convert through. In probably 90% of liberal conversions, the community rabbi is the obvious (and only) choice. He or she will convene a beit din made up of either other rabbis or respected laypeople in the congregation. Some of the larger Jewish communities have larger liberal conversion processes. For instance, the conservative community in Los Angeles has a very streamlined program through the American Jewish University.
For orthodox conversion candidates, the question is much harder: RCA or not RCA? The Rabbinical Council of America has attempted (controversially) to streamline orthodox conversion procedures in order "to comply with halacha" and to presumptively qualify as valid conversions for the Israeli Rabbinate. The Rabbinate has agreed (until they change their minds) to presumptively accept conversions performed by the regional batei din overseen by the RCA. On the other hand, some conversion candidates don't agree with RCA rulings or otherwise don't wish to have an RCA conversion. (Keep in mind that the batei din on the RCA list are not all in the same stream of orthodoxy. There are chareidi and other non-Modern/Centrist Orthodox groups on the list, if that is the type of conversion you would like. Even the more Centrist/General-purpose Orthodox batei din allow you to "personalize" your conversion through your choice of shul and sponsoring rabbi.)
Others who choose not to pursue a RCA conversion simply have a community rabbi or community beit din willing to convene a beit din without all the fuss and hassle of traveling to an RCA regional beit din every three months or so. (The closest beit din could easily be several states away.) If you plan to have an RCA conversion, most American orthodox rabbis will understand why, and most of those rabbis will support the choice. Many community rabbis stopped performing their own conversions after the new RCA procedures were adopted in 2007, so your community may determine your conversion options. Note that many chareidi communities have their own beit din that will still perform conversions. However, read below to see how those conversions work for aliyah.
I suggest having a frank discussion with your community rabbi about the choices available to you and the pros and cons of each. Keep in mind that RCA conversions are now so difficult, so well documented, and so regimented (and not to mention lengthy) that it's pretty unlikely that a convert who remains orthodox (even if he or she moves to a different stream of orthodoxy) will have the conversion questioned. That in itself is a good reason for going the RCA route. You know your conversion will be thorough and widely accepted. I think the procedures in at least some of the regional batei din could be compared to a year or more in seminary or yeshiva. Personally, I like that, even though it makes the process longer, more difficult, and more expensive. (The $25-50/hour for private tutoring is probably the single most expensive element. Imagine a weekly hour session for 1-3 years!)
The take-away of this point: think about how you would react if someone rejected your conversion as valid. What if they denied you from taking a class, joining their synagogue, or rejected your child's application to a Jewish school? This should inform your choices, but it should NOT be the deciding factor; go into your conversion with your eyes wide open. You're never going to be "ok" with someone rejecting your conversion, but you will still have to come to terms with the possibility (some would say inevitability). Unfortunately, most people let this factor decide for them, potentially leading to a great deal of frustration and unhappiness. On the other hand, whichever movement you choose, make sure you actually want to be there! Choose the movement you believe in, even if that means dealing with more flack from people than you'd like. It's a lot easier to handle the flack and stupidness when you're happy with your choices.
c) How "good" the conversion is for aliyah purposes.
As I noted in the converts and aliyah post, you can have the strictest conversion in the world and still "fail" to be Jewish for aliyah purposes. You can read more in that post, but the general rule is that a conversion from any movement is theoretically valid for aliyah (for government purposes, not Rabbinate ones). The trick comes with satisfying the government regulations that have created additional requirements: 1) living in the converting community for a year after the conversion is final and 2) a minimum study requirement of 350 hours. (These requirements are presumably retroactive to conversions performed before the regulations existed.)
Going back to the RCA/Not RCA conversation above, I mentioned that those regional batei dins are presumptively accepted as valid for the Rabbinate. On the Israeli "approval list," (listed at the top of the Links page) there are some non-RCA batei din listed and accepted. Their conversions will also (until the Rabbinate decides otherwise) be accepted as presumptively valid for the purposes of the Rabbinate. As all of you probably already know, any liberal conversion is presumptively invalid for the Rabbinate (and by presumptively, I mean Hashem might have to speak from the Heavens to get them to accept it). But what if you convert with your local orthodox rabbi or a community beit din that isn't on that list? Your conversion may still be accepted as perfectly valid (and the more chareidi your beit din, the better your chances), but those conversions are individually "verified" as being halachicly valid. I don't know what that would entail, but it's one more hassle I don't want in my life.
Good luck making your very important choices. And if you change your mind, you probably can. It may happen during a conversion process or after you've completed it. However, you may lose a lot of time. If you're single and want to try to have children, that could be a significant factor for you. Of course, you don't want to make a decision for the wrong reasons and then have a spouse to deal with when you change your mind! (But for the record from the person who works in divorce: divorcing "because of religious differences" is unlikely to be the real culprit. It's much more likely to be a more foundational problem like lack of communication or poor money management. For full disclosure purposes, I blame almost all divorces on those two issues, abuse, and cheating.)