Scooter

Only bike I'm riding at this time
1985 Honda "V665" (1100cc)
Quick enough for me - does the "ton" either top of 3rd or in 4th
Enough power that you can skip gears on the way up 1-3-5-6th.
Like all V4's... linear power, no peaks, just like a big electric motor
Shaft drive for easy maintance, but it jacks the suspension some.

Only modifications:
Wider wheels (welded up to be an inch wider than stock) with what use to be, sticky tires.
Handlebars replaced after minor spill (other driver ran stop sign)
Similar rise and bend to the stock ones.

A bit much rake for fast backroading, but that's fine.
Nice and stable