I'm a huge fan of the Heize Baby Basics "Toddler Straw Cup". DS has used this for months now and finds it very easy. I've had several friends that have also had very favourable experiences with this one.

I never bothered with formula top-ups. Initially when starting solids if DS didn't have much then I'd see if he wanted a BF straight but as soon as he was eating a reasonable amount I'd stop that.

NB I haven't had a problem cleaning the valve. You pull the whole plastic piece out and then you can see the little clear plastic membrance that sits over the hole that is the valve. That membrane can be easily slipped to one side so then all milk/formula can be removed.