Hydroflask gets my endorsement because they have thick insulated lids (which makes a big difference), and they don't have any parts that are hard to clean. REI seems to have the best selection and prices, but they do also have them on Amazon.
I literally don't use regular cups at all anymore — a thermal mug keeps milk icy cold, beer frosty, and tea or coffee toasty warm. The general idea: keep your beverage at the perfect temperature longer.
I think the 12oz Hydro Flask mug is probably nicest for people at home.
You can even put your ice cream in a thermal mug or food jar to keep it from melting before you're done! (as a matter of fact, I have a Thermos food jar that I scoop a pint of ice cream into and store in the freezer compartment of my mini-fridge and it stays frozen and fresh instead of turning into a goopy mess via the melting/freezing cycle.)
These are expensive enough that you're probably not going to want to use them for a large gathering, but if you've already converted and have a collection, I'd put them out by the
You can also get party cups that are insulated, though obviously less-so. I've seen brown rippled ones that look great for an event.
When the outside temperature is either hot or cold, that can cause your drink to lose its temperature much faster, and is also a time when a cold refreshing beverage (or a warm soothing one), is that much more appreciated. I bring thermal mugs, but also thermoses: chilled white wine for a concert in the park, hot cocoa for star-gazing, or just a way to keep your freshly brewed camp coffee hot for the stragglers.
Additionally: I don't have one myself, but for keeping things warm, I think the ratings are now good enough to justify gifting the new 14oz Ember Mug to a loved one who nurses their hot beverage of choice.