Which is really better A/D+ or B/B+ at 3B? Would the differance in errors counter the + - plays and dp chances?

pre-update I would have gone A/D+

at 3B given the relative lack of chances I'd go B/B+

I'd guess a slight downgrade in hands is more than offset by a huge upgrade in range. Think of it this way - a substantial number of the errors the B/B+ guy makes are on balls that the other guy wouldn't have gotten to. They were going to be hits anyway. The error is also going to keep the ball in the infield the vast majority of the time, whereas the ball not-gotten-to goes into the outfield, giving baserunners the opportunity to move up more than one base.