Good testing centers: Any that are near to you. The only ones giving the test are prometric centers, so you have no choice there. Might as well go to a closer one.
Yes, you can figure out which testing center you want to take it at. There's a "locate center" option on their website...in addition, you don't pay prometric anything. You pay ADA. Which reminds me, you have to acquire a DENTPIN first, then use that DENTPIN to register/pay for the test through ADA, then they'll tell you that you're eligible to test, then you schedule your test through prometric's website/phone line.