I'm also wondering the same thing - we use the Nuby's as well. Had such a hard time getting him to drink from a cup in the first place, and those were the only ones we had success with.
I have heard that it is better to drink from a hard-spout cup eventually, and even removing the valve so that the liquid flows more freely, giving your lo the feel of taking an actual "sip". But I really don't feel like ds (or my hardwood floors!) is ready for that.
Does anyone have a recommendation for a hard-spout cup that is easy to clean? That is why I like the Nuby's so much - there are no annoying valves to deal with.