yea, I agree with what the above guy said. Most gyms will take any of the big certifications, but some pay more or require you to be certified with the more respected ones like ACSM and NASM. The information you learn in all the certifications is ok, their good to brush up on your anatomy and learn a couple formulas for calorie intake, but as far as training they are pretty useless.
The big difference is whether they are proctured or not or reqiure a degree to sit for the exam. My cert with ISSA allowed me to study and take the test online, so it was easy and convenient, but gets bashed because the whole test is pretty much open book, so you do get a lot of idiots walking around as "certified trainers" who have never stepped foot in a gym. Reguardless, Personal Training is not federally regulated yet, so no licence or certification is required to call yourself a trainer.