Hey Kane, just saw this.
My advice is to go ISSA right now. Their focus is much more on educating their trainers with a basic level of knowledge before testing, while the NSCA tends to focus more on certifying already proficient people (that was my impression anyway, someone feel free to correct me if that's changed recently).
Both organizations have great support resources in online boards and very knowledgable faculty, but I'm rather partial to the ISSA because Dr. Hatfield himself hosts his own board on which he posts and answers questions nearly every day. He also offers free support software (calculators and what not) to ISSA certified trainers. There's also a ton of other very knowledgable folk that post on there regularly; I'm sure there are on NSCA support groups as well, but I've never posted a question someone couldn't direct me towards an answer to or explain themselves on the Doc's board.
That being said, NSCA is a bit more recognized in some areas of the country. If you can pass the test and are proficient now, it might be the way to go. Marketing is sadly a big part of being a trainer these days, and the customer's knowledge of your certifying organization is going to be important, especially since you're so young. I'd advise calling some local gyms and asking what they tend to prefer to get a feel for who's more popular in the area.
Just to add to the confusion, the ACSM just came out with a personal trainer cert. as well. If they're big in the area, they're definately the way to go.
Hope this helps,