Not going to vote, as I use them for completely different things.
PearPC: Optimized for running OS X, does the job well and painlessly. Easy to set up and run, and "Just Works" for OS X 10.1-10.4.
QEmu: regarding running OS X in qemu-ppc, doesn't handle networking all that well, doesn't display correct colors on all target builds, and while it's catching up to PearPC, it's still slow.
Otherwise, QEmu is an excellent testbed for running code and testing it on different architectures. It's fairly easy to create a front end for it (I prefer the command-line binary + front end approach to the all-in-one approach in general), and it has active development and an in-depth feature set.
Of course, I also find that with half the qemu builds, I can't actually get them to compile correctly in my build environment. With PearPC being so stable, this hasn't been an issue.