It’s a staple of the Star Wars movies. The ice planet. The desert planet. The swamp planet. From pole to pole, it’s one climate all the time.
Only this doesn’t really work in real life. You might get a desert planet, but it’d be barely habitable if at all. Same with an ice planet. A Hoth in the real world (real universe?) would be habitable only in a limited area. And a swamp planet?
As noted crime author Charlie Stella might say, “Fuhgettaboutit!” It would have to be temperate all over.
So what’s the most realistic planet we can use in science fiction? Simple. Go look out your window. Now think of a place that looks utterly unlike where you are right now. Now think of someplace else different from that. Imagine a place that could support all those climates and landscapes. Can you think of one?
Now on distant Earths, one climate might dominate over the other. Warmer planets might have more swampland (assuming the life forms evolve). Colder planets could be icy, but quite likely, they’d be a lot like Mars with warmer weather (and let’s hope a magnetic field.) But that dominant climate won’t be the only one, or even the majority of the surface. Plus, factor in different gravity, distance from its star, size and number of satellites, the star itself. Plus, you can go to town with something that’s been normally the domain of fantasy writers:
Making your own map. The layout of continents can affect how a planet evolves much the way they do on Earth. And really, what SF writer doesn’t want his or her own Mordor?
Really, if a planet is going to be habitable to humans, there’s a 90% chance it’s going to look a lot like Earth. ‘Cept different. And that’s where you can really start to have some fun.