What is a good alternative to Pristiq?

It depends on many things: what you were taking Pristiq for in the first place, what dosage, what you've tried before, what side effects you suffered from with Pristiq, etc. The best alternative (as in, most equivalant switch) would be Cymbalta which is the only other approved SNRI (subtype of antidepressant that includes Effexor, Pristiq and Cymbalta). Effexor also, but Pristiq is the "upgraded" version of Effexor already (as Lexapro is the "upgraded" version of Celexa).

Only a doctor can determine which is the best alternative for you.