Toddler needs a closed bottle/cup for milk : what's best for his teeth ?

Hi everyone !

Although I've been told that an open cup is often recommended right away when a toddler has stopped nursing or drinking from a bottle nipple...

What is best for his teeth when it comes to drinking from a *closed* container ? Soft straws, 360 cup (I hope not as cleaning milk from these seems awful), cup with a soft spout, hard spout, ... ?

My toddler has pretty good dexterity for his age, is learning well with a spoon, fork, other utensils, he'll drink from any container with zero issues. But the slightest distraction can make him spill his drink. I don't mind it when it's water, it's just a learning experience, but cleaning milk is something else. Thank you so much in advance.