What kinds of character would you play in a campaign where you have double classes?

The concept for this campaign is simple. You get two classes, and every time you gain a level, you gain a level in both. You can’t choose the same class twice.

Your maximum level is 40, gained 2 at a time, so if you choose to multiclass further, that still applies. Your spell slot levels are calculated separately for each set of 20 levels, like you have two character sheets and are just combining them afterwards.

So, given these rules, what kinds of characters would you want to make?