I like the die with the collet, though I know there will lots of others who prefer the hammer. Hard for me to disagree with them as I have never actually used a hammer.
The only problem I have with the collet set up is that sometimes the neck of the cartridge is holding the bullet so tightly, that when you tighten the collet enough to pull the bullet out, it leaves a significant and unsightly ring on the bullet. I know that most often the bullet can be used again, with little or no effect on its path or velocity, but to me, it just looks like shyt. Unless the ring is very very faint, I usually toss the pulled bullet ... so it can get costly, but if I have to pay for my mistakes, I'm more likely to learn from them.