Have covered this subject considerably elsewhere, but in general if you don't want to bother with sorting or turning case-necks, Lee Collet dies are the best deal.
If you want the absolute best accuracy, however, some sort of bushing die works even better--IF you sort or turn case necks, and do NOT use the expander ball.
From my experience I'll add another IF:
If you aren't having to size the necks down more than 4 or 5 thousandths.
