I have tended to play or run longer campaigns, but the few one offs I've played in have been great to try out different classes. Generally I think that they're pretty low effort in character creation, the DM can even provide premades for players if it's also a brand new system and you're wanting to get into playing straight away. When it comes to DnD, it also lets you try out those higher levels from time to time, I think last campaign I ran players hit 7th at the end of it and the one I played I reached 8th so it was fun to play in a 12th level one-shot where I could try out a high level paladin.