I like having a bit of a variety, though I have a bit more variety than I would like from when I was trying to figure out what worked for DD1. Now I just what I have. Our main stash in her current size is a dozen pfs, about a dozen flats, and a few OS covers and some wool. I also have 5 Simplex for the diaper bag and 3 Grovia AIOs, which I basically hate, but keep for the rare times I need regular clothes to fit her. We also have a full stash that doesn't fit her right now- some MEOS and 10 BG 3.0s. I can't get any of those big enough for the thighs without either gapping at the waist or coming up to her armpits. But I won't get rid of them because I'm sure they'll fit again one day and then I'll want to use them.
Basically, different diapers have different functions. The fitteds are great for under wool in the summer or when she's a little rashy. The Simplex are so nice for the diaper bag-only one thing to keep track of. The pockets are great for having stay-dry at night (until she outpees their stuffing capacity). And the pfs and flats are such low maintenance that they're the staple of our stash. I'm using them right now exclusively so I can slather her little rashy spot with Triple Paste and not have to worry about it not washing out.
I started out with DD1 with only 1 diaper type (BG Organics), but quickly realized that just wouldn't cut it for us if we wanted to CD full-time. They didn't work for nights or naps (DD1 screamed her head off the moment she felt wet), they were high maintenance with the wash routine, and she outgrew them at 7 months old. So we diversified, and life is much better now.
Rebecca, married to J (2007), DD1 Anna (11/09) and DD2 Ada born at home 7/12 DS Henry born at home 3/14