We found that a Cannondale T2 was the best fit for us. 6'1" Captain and 5'10" stoker. There is plenty of adjustment in the rear with that frame so that our shorter kids could ride back there with just the drop of the seat post. We also fit well on a daVinci but opted for the Cannondale.
At first, we looked at a few KHS tandems but all of the frames were too large in the rear to accommodate.