A lot depends on your level of ability. I have skied all three and found Borovets and Pamporova best for beginners. Borovets has much more night life though. Bansko is better for more able skiers and the prices in the local bars were ridiculously low.
Remeber though that everyone will have their own opinion. Read the resort info and make your own mind up.
send me an e mail I will get you some prices if you want as I am a travel agent Ive dona all 3 resorts and my fav is Pamporovo and the night life is good just as good as borovets!! We are going march 3rd next year and cant wait!!