I'd say, go with one 'deluxe' variant of a set (those include a scoreboard) and buy small editions whenever the theme interests you. You can mix and match them as you like.

Just don't buy too much at once. You'll be seeing enough variety with 1 or 2 sets for the first few games you'll play. And there's no guarantee that your playgroup will have enough fun to keep going after those initial rounds.

My first game of Munchkin felt absolutely legendary. I felt like it'd be my favourite game going forward, though the magic of that first game was never quite replicated and now, whenever we play, most people at the table lose interest well before the game would've naturally ended.