Depends what sort of thing you're after. Me and my old man went with
http://www.britishbiketours.co.uk/ at the beginning of May. We did the black forest tour. Worked out about 200miles a day. Maybe more on some days but you're there to ride bikes! I think we finished the planned days riding early on one of the day so we got a whole heap of more riding it. I was expecting it to be proper **** (full of old blokes, pipe and slippers etc..) but I really enjoyed it. Good mix of people in the group, different abilities etc.
The other company which I have heard good things about is:
http://www.horizonmotorcycletours.co.uk/ but I have not been on a tour with them.