Something used and relatively inexpensive. You don’t want to jump in with a huge investment until you know if it’s something you like. If you look around Facebook marketplace or Craigslist you can find decent deals. If you have never been on one, you might want to try one out a tour company. They usually have moderately powered sleds that are set up for easy learning.
As for specific makes/models, I really like Ski Doo 4 strokes. For a beginner, they are reliable, easy sleds to learn on, particularly the non-turbo models. My wife and son have both had 600 ACEs. They are a very good sled for beginners. As you gain experience you can move up to bigger motors like @WinterWolfand @dryslothave. There are too many stories of newcomers hopping on powerful sleds that they can’t control ending tragically.