Hmm, I don't remember any mini games from any MP game but MP4, but let's see... I really enjoy the explosion effect from Bowser's Bigger Blast, it cracks me and my friends up. You see them fly off, and then down in the foreground...
But in regular mini games, like the ones you play once a round, Dungeon Duos is the best. Especially if you have a turbo button.