Advice needed: cups

I think it depends on the formality of your event and what you're using for the rest of your dishes. Plastic cups would be out of place at a formal or semi-formal event, especially if you're using real plates and flatware.

You could do both if you want. let the people choose which they prefer. i thought about these ideas as well but ended up doing koozies instead.

This is what we ordered for our champagne toast and for guests on Amazon. They're not personalized, but they're not likely to break and are still pretty (and reusable/recyclable). You could add a personalized sticker maybe. They also sell wine glasses: