I had a 1999 Triumph Adventurer (885 cc) that I think was tuned more for torque than most Triumphs at the time. A triple cylinder, of course. I averaged 51mpg US with a mixed riding style (half "spirited, half conservative). I now have a Kawasaki Super Sherpa (250 cc single) that is ridden more on the "spirited" end (to get any performance at all, heh) and I average 77mpg with it.
I also had a Buell Blast that is supposed to be one of those mileage kings but I didn't ride much because it was just too weird for my taste. The long stroke engine cried out for a wide ratio gearbox but as far as I could tell it was narrow ratio and annoying. Seemed like it always needed shifting. Or something. Anyway it didn't suit me.
I have been drooling over those Honda 500 twins and the 300 cbr but I will stick with the Sherpa for a while because it just begs to please...
Technically I like a twin with a single carb or fuel injection body. Not too many of those around, I guess. NC700 and a Guzzi Quota (I had one of the latter too). Can't think of any others...
BTW it is interesting how closely the NC700 matches the old Norton 750 Commando. Undersquare twin, about 60 hp, redline around 7000. My Commando was no slouch; I wonder what the NC700 is like to ride. The article I'm reading says it gets the same mileage as the cbr250r!
http://driving.ca/honda/nc700x/revie...onda-nc700-x-2