Well you shoudl go find out what certifications that your gym accepts, as you said there are many out there and there is no point in getting one and paying all that money if your unable to get a job with it.
These are my opinions on some certs. from either having, research or speaking to others on it. most of the widely recognized certs have different locations that you can take a 2 day course in. Also most of these different certs have idffernt types of things you can get this is just talking about the most basuic being a certified personal trainer.
ACE is well known but not that hard to get and not all that comprehensive
ISSA is pretty good but a little pricey but well worth the money.
NSPA (the one i have) wish i hadn't wasted my time with it i honestly feel it's worthless but i went through the gym to get it so i thought i'd be good to have. i plan on getting something else more substantial later on.
ACSM i have heard this is very comprehensive. I had a friend who actualyl took a smemester long coruse jsut to prepare for this one.
Also something else you need to realize is, is that a personal trainer is only as good as his/her knowledge outside of the certification.