That weird bottle funk drives me nuts too. With my kid’s water bottles, I’ve noticed it’s almost always the lid or the gasket that’s the culprit, not the actual stainless part. Even after running them through the dishwasher, sometimes there’s still a hint of something off. What’s worked best for us is popping out every removable piece—especially those silicone gaskets—and soaking them separately in a baking soda paste or just boiling water (careful with any plastic bits). It’s a pain, but it really helps.
As for those UV self-cleaning bottles, we tried one when my son was in the hospital and I’ll say... they’re decent at keeping clear water from getting funky, but they don’t do much for old smells that are already stuck in the lid or gasket. You still have to clean those parts manually. I wish there was a perfect material, but honestly, it does feel like a “pick your poison” situation. Stainless is our go-to just because it survives rough handling, but I totally get your frustration about lingering odors. If you ever crack the code on a truly stink-proof bottle, let me know!