I actually prefer hour as it's more money and it gives us time to chat about random stuff. When I have clients come for 30 minute bookings they always over run by 10 minutes or so as we are so busy chatting to get to know each other a bit. 

I might start offering 90 minute bookings for when an hour isn't long enough but 2 hours would be long :-)

I prefer shorter ones like 15 min or 30 min though at times I have an hour or 2 hours booking and we will just be chatting most of the times.