Stainless steel or plastic sippy cup—which is better?

Reviewers say it's a trade-off: insulated stainless (Zak Kelso stainless, Tommee Tippee) keeps drinks cold for hours and avoids plastic taste, while plastic versions are lighter, cheaper, and easier for the youngest hands. Low-plastic-focused communities like r/moderatelygranolamoms lean stainless or glass; daycare and travel users often keep a plastic set for durability and weight.