id say any honda ujm in the 600 up range. You can get em cheap to free they run forever and are fairly cheap to operate. Craigslist your area for cb750s

Vstroms, BMW GS's and alike are lot more comfortable than his Buell.

My wife has been on the back of a Z1000 and a 919 with me as well as an XB12s.

The seats are better and bigger on the Jap bikes. Other than that they are pretty similar from the back seat. The Honda has undertails which can get a bit warm.

Have you thought about a Triumph Bonneville or Thruxton?

Those aren't dual sports, they are adventure tourers. Dual sport is a KLR/DRZ/DR type bikes

stay away from FZ6, suspension is junk. FZ1s are nice.

So are Goldwings, Visions and Electra Glides.

What's your point?

Z1000 are very comfortable. I had a Z750 before my GSXR and it was fun and easy to commute on. The suspension isn't that great especially for 2 up but You can fit a 636 shock on it an improve it greatly.

I totally didn't read all of that either. You want your girl to learn to ride on this bike? Hell, a good two up bike will by definition not be a good beginner bike. You can have "ok" in both categories, but what I would classify as "good" would be conflicting in both categories.

more expensive than my pick but a good used bonnie would happily fill all the roles hes looking for

Shit. Even I forgot about the learning her to ride..

How about this, what's a good beginner bike I can teach her on, ride to work, and cart her around on if she decides its not for her?

The Kawi Z750 is a great bike to learn on. The power is very tractable. Peak torque is at a relatively low RPM (about 6800) so you don't need to wind the engine up to get it to go. It has enough power on top to have fun on it though.
They are heavier than a 600SS but the HP is about the same approx 110HP and torque is around 55ftlbs. A slip-on, air filter, and PCIII help tremendously with power on top.