Huh??? You mean, which feels best while holding it?
I would vote for any 2xCR123 light such as the Surefire L4 or L5. 2xAA lights are too slim, 3xAA are too long, 1xAA are too short, 1xCR123 are better, and any C or D lights are too fat. 2xCR123 are just right.
I like 2 cr123 bodied flashlights the U2 is a bit bulkeir than most and fits my hand well also 18650's will fit in bored out bodies, which will lower the wieght but I say that length doesn't matter but I think anything bigger than a cr123 bodied light would be a little big but there are occasians when an M6 would feel fine (it's not like they ar eany bigger than a mag 2D.
Well, I was actually thinking about this today. My E1L feels perfect in the hand and is the perfect size. Its not the best pocket light, a bit too big for me, but in the hand its great. I like that surefire heads are a bit bigger than the tube. Can't wait till they make one with a cree.
My $30 Huntlight FT-01PJ feels perfect to me. Just the right size and weight. It too uses 2 CR123a. My P1D-CE is too short to hold comfortably. My 2 C cell TaskForce Luxeon has too great a diameter to hold comfortably.
I guess I'll be shopping for another 2 CR123a light. It will probably have a next generation LED with nice build quality but still must be a good buy, such as the Huntlight was.