We started with an open cup with handles, not doidy, but still open at 6 months. It's easiest by far to actually sit BEHIND your LO- or stand behind- that way you can provide hand over hand guidance on the handles, which you need to at first, and you can tip it and see what is happening with the water. Give it a try- i tried both in front and then behind behind MUCH better!!
We introduced a straw cup rather than a sippy cup as another travel option (open cup messy..) and that has worked well for us!