Both are excellent choices. We have run Biondo 85 and 450 for a while now. Seem to be a little more user friendly with bigger key pad. Just my opinion.
I have drove a couple cars with Dedenbear boxes and I have Biondo boxes in both my cars. Personally, I think the Biondo boxes are Easier to operate and excellent quality. I have a mega 450 in my truck and a mega 85 in my dragster.
K&R offers some nice features. Only thing I don't like are the little toggle switches. Biondo by far makes the most user friendly box out there for a racer.