I've got 7 for the pre-army builder waves and 8 for post-army builders. A few of the army builders can be displayed different ways so I take advantage of that when possible. (Hydra agent, Shield agent, etc)
Of course there are TRU waves, some have 4 exclusive minimates, some have 2 (earlier waves) and some have 8, then you've got box sets which usually come in 4 so if you've got 2 together it makes an even 8.
I think 8 is the way to go which is why I'm stoked for Luke's 8 figure stands (see the thread in the "max blanks and other minimates" forum)