by I Eat Tables
I've played 2, 3 and 4 character seasons, and I don't think I can explicitly say any single way is "best", same as albcann above.2 character is less complex, and functionally slightly easier, so if that appeals it's an argument for it. In a 2 character game you generally can't have each character specialise too much - with only two of you, you need to be flexible and ready to adapt.
3 character depends on how you collectively feel about controlling an extra character between you. It adds a bit more complexity and difficulty, but the advantage is it makes more specialised characters feel better, you can have a character who is very good at one thing and focuses primarily on that during the game, rather than being a jack of all trades. I do think 3 is a good number to aim for if you're comfortable doing it, as it makes things a bit more interesting in my opinion.
4 characters has the advantage of giving each player 2 characters, so there's a nice divide. It also further makes specialists more viable and fun. It's also the hardest way to play, so if you prefer making the game a bit more challenging you can consider it.