If you're willing to buy the supporting equipment, LiFe packs are the way to go for flight packs.  Nicd's are old technology.  Nimh's are good if you're not doing crazy big stuff with high drain digital servos.

I found myself in your position a year ago.  I had enough high capacity chargers, that I have stuck with Nimh's so far.  As I cycle through batteries, I'll probably eventually switch to LiFe packs.