We use the Miracle 360 cup
You're going to have to watch any type of cup for "hidden" mold. The Miracle 360 cups can get mold in the top if you don't completely disassemble and wash well. Sippy cups can get mold in the nooks and crannies. Any cup with a valve can develop mold. A silicone o-ring (like on coffee mugs) can trap mold if it's not removed and cleaned. You just have to be diligent with cleaning. All the straw cups I have for my kids are clear/white, so mold would be very noticeable.
My kid only drinks out of straws. 😅 He hasn't been able to use anything else consistently. But if you change your mind about straws, we use some nice silicon ones. They're more like water bottles but smaller.
Reflo smart cup open cup or munchkin open cup
@Kate I’d like to know which ones you use please! We love the silicone straw cups over here
We loved the mushie brand of sippy cups.