I haven't built a B class version yet, but my A class design is basically a heavily modified Battle Floyd. They fly great, and with a few changes are actually very durable for their size. I do think a Floyd in B class is dead meat if built stock. (have a picture around here somewhere to prove it)

I'd say the spads are good options. There seem be a few guys flying HORs in B class with success.

The key is weight and wing area. Whatever you build, the lighter the wing loading, the better your turns and overall performace will be. So keep it light and put on the biggest wing you can manage.