I like singles and would prefer one to a twin, 3 or 4 for some applications
I really wanted to like the the Yam's but they just 'don't' until you gear them down (maybe combination of too high gearing and too much weight?)
For some reason the Honda XL/XR motor felt a lot faster?
Looking for an older style (pre RFVC) XL/XR500motor as it slots right into CB360 chassis (I only know because I had one stolen and when it was recovered that's what was in there)
DR BIG (Suzuki DR800) would be the thing to have, they haven't made the 800 for a long time though.(got a book where a German guy put DR800 motor into RG250 chassis, I know how well RG250 goes round corners 8) )
The LS650 'Sausage' has a couple of issues if you rev them (main bearings, cam chain tensioner) but will thump along quite happily within 'design parameters'
Never been a fan of the Kawasaki motor, always sounds like the big ends are knocking, even when new? (no idea why, haven't been 'inside' one)