I shudder tho think how much I've spent on sippy cups ... I think we've got one of everything! The one that I've found best for DS is a Tommee Tippee cup with handles and a flip-up spout. No idea what it's actually called.
I think it really depends on the child, but I found DS was no good with any cups with a valve which pretty much eliminates all non-spill cups, except these. He uses it really well now, and can manipulate the spout himself to seal and unseal the cup. The only downside is that it doesn't hold a large volume - but he only has water in it so it's easy to refill wherever I am. Plus side is that I know he's drinking fresh water.