Whats a better 2 up seat on a 06 Streetbob:
HD touring or an HD Sundowner solo with passenger pillion? Any opinions would be appreciated

 

I really liked my rack with the passenger seat that went on top of it. Got good feedback on comfort, too. Looks great when you take it off for the solo look.

Downside is the huge cost

 

I bought a mustang seat for my 08 street bob. It pushed me back 2" in the saddle which really helped me stretch out on the bike. Most comfy seat I've ever sat on.
I've got no experience with the seats you mentioned however the mustang has a removable passenger pillion which really isn't very big. A larger person may not like it.
My old lady and kids don't mind the pillion. Mind you they never had an extended sit on it either

 

I run a stock Fat Bob seat on my FXDB. For short runs my wife doesn't mind it, and it is also a great seat for solo riding on the Street Bob.

 

It is really a personal choice, I now have 2 2-up seats and 3 solo's. The FB orig. seat is ok for short rides , but I got a deal on a used sundowner and that is the one I use for the OL rides.