I prefer to have planted, moderately stocked tanks with small fish. Right now I'm in the middle of getting ready to move, so I'm selling fish and tanks, and everything is a mess and all of my tanks are overstocked. It's driving me crazy!
I've done the big fish, big tank, big filter situation and I find I prefer set ups under 20 gallons with micro/dwarf fish.
As for the mbuna, I had an 80 gallon set up with 10 fish and lots of rock without problems... until I went on vacation. I think it depends on what species of mbuna you stock with. Labs and acei are not nearly as aggressive as kenyi and auratus.