Since I started my stash which includes each of the above, I've come to like both for different reasons. But, I'd like to know your reasons for choosing if you had to choose only one.
Nutmeg, cilantro, sage, mint, thyme... these are a few of my favorite things!

We have four children; one left us too soon.
Re: If you had to choose only one: FB or BG OS pockets? Why?
Personally, hate BumGenius with a passion.
They fit horrible on my son, I don't like the feel of the fabric, the inner PUL was always still damp when I line-dried indoors, hate the inserts etc.
Fuzzibunz I absolutely adore and there is not one thing I don't like about them. I think they are cuter, they are softer, the colours are nicer, they dry SO fast, they are easier to stuff,,I could go on.
So..if my answer wasn't obvious; if I had to go with one, Fuzzibunz.
We'll miss you sweet Debbie Girl (4.21.12) and sweet Cindy Girl (8.9.12)

I love my BGs and my FB is just okay. I do like the interior of the FBs, but the fit, colors, aplix or snaps option all go to BG for us.
I don't really care for the FB way of adjusting size with the elastic and buttons. I just think it's a pain.
I would get a couple of both and see what you like, rather than get all of one. I still use my FBs, just prefer the BGs.
Missed m/c 11.09 | Missed m/c 3.10 | We miss you & love you so.
~ ~ ~
Formerly toddandjulie
FB. I have a couple of BG pockets but I really don't like the microsuede and I think the FBs fit better, dry easier, and are generally superior to my BGs in every way.
Though I do love the BG Elementals.
Without a doubt BG. We ended up selling all of our FB. They were fine diapers, but I had so many wet issues with them that I don't have with any other diaper. I'd either have to double/triple stuff them, or just put on a different diaper.
That being said, it's different for every person and every baby. My stash is not all of one thing, and I wouldn't want it to be.
I have both and like them but prefer the BG.
Like a previous poster the elastic on the FB is a giant PITA. For some reason I also have a harder time getting the stuffing all the way in and we've had issues with the insert where it slides up her back and gets her wet when she's in her carseat even when I'm positive I had the insert stuffed all the way in.
This exactly! We bought more BG's because of the fit and ease of adjusting sizes. Our FB's are ok...but for daycare and daily use we always choose our BG's. Our daycare provider finds it easier to use the velcro instead of snaps also.