The one thing worth knowing before you buy any set of tumblers is that weight matters more than looks. A glass that feels thin and light in the store will feel exactly as thin and light in your hand every single day, and it'll be the one that chips first on the faucet or the edge of the sink. Pick them up before you buy them. If they feel like they'd lose a fight with a dishwasher rack, they will.
If you've got none to your name, or just a mismatched shelf of leftovers from three different sets, start with a basic double old fashioned size, something around 12 to 14 ounces, in plain glass with a heavier base. That size covers water at dinner, a soda with ice, a whiskey if anyone's having one, and it doesn't look out of place doing any of those jobs. You don't need the tall ones or the short juice ones yet, those are a second purchase once you know how you actually drink at home. A set of six is the right number for most households, enough for a weeknight and enough for two people who had people over and didn't wash up right away.
These work everywhere, but they really earn their place in kitchens that double as the everyday dining spot, and in smaller apartments where one glass has to do the job of three because there's no room in the cabinet for specialists. Summer is when they get used hardest, iced tea and lemonade and whatever's cold in the fridge, but a good tumbler doesn't care what season it is, which is more than you can say for most glassware with a seasonal personality. A heavy household, kids, a dog that knocks things off tables, does better with a thicker, more forgiving glass than with anything delicate looking.
Plain clear glass is the easiest finish to live with, full stop. It goes with every dish, shows nothing in particular, and replacing one when it breaks doesn't mean hunting down a discontinued color. Amber or smoked glass looks good on a shelf but shows water spots in a way that'll have you rewashing glasses that are already clean. Colored glass is fun for two or three accent pieces, not for the whole set, unless you enjoy the specific disappointment of one favorite color going out of production the year after you bought it.
Would I actually want to wash this one by hand at ten at night, or am I buying a glass that only works if the dishwasher behaves itself?