I have both. An Onan 2500 in the TC and a Honda 2000 I use with the TT. My Onan in this TC is quiet, probably about the same as the Honda. The one in my previous TC was much louder.
The Honda runs the ducted Dometic A/C in my 28' TT without an issue and of course the Onan in the TC also runs its a/c.
Convenience-wise the fact that I can push a button in the TC to fire up the genny is very nice, but I agree with the comments about it consuming lots of propane (about .6 gal/hr.) That means that just keeping the batteries charged while winter camping with the heater also running will run you out of propane quickly. If I make any winter trips with the TC I'll probably take the Honda along and use it on the TC.
