lol. i just went through this whole thought process myself. I thought of doing a 6-12 gallong little saltwater set up. Have a clownfish. Some anemones. Maybe just some harlequin shrimp. But then i just decided i'd much rather wait for the time/money/space for a larger tank to put a cute dog faced puffer inthey're possibly my favorite.
Bigger is better but if you can handle the maintenance then a small set up works.