from what i hear the best ones are the hotlips mags with the metal feed lips. i picked up one of them with the plastic feed lips and ran about 50rds through it with no prob. you can pick up the plastic lips at academy for 20 bucks but ive seen a few places online for the steel lips for 30 i think.
I've gone through many of the HotLips 25rd magazines. If you load them by hand, they last about 5,000 rounds. If you use the Butler Creek quick loader, you can chop that in half.