There is nothing wrong with 4 teams per division IF you don't mind playing your 3 rivals 30 times a year. Otherwise, I'd go with 2/8.
I went to 36 teams because I'm a nut and wanted a perfectly balanced schedule. I have 3 divisions of 6, no inter league, no DH, 2 wild cards (one game series). Teams play division rivals 18 times (other division teams 6 times).
That said, it was an imported game and I've decided to do it ALL over again in OOTP 19. It's a LOT of work, but it's worth it.
The goal is to have fun and if you don't like what you do, you can DO IT AGAIN!