i have a h51, i preordered a sc51, and i also have a d11.
the h51 is a good combination of spill and throw. works on aa. can be used in the hand, on the headband, and comes with a rubber type clip. the click button is nice.
the d11 is pretty much all spill, and has no shortcuts to low/high (or medium for that matter like the h/sc 51. using a 14500, the d11 appears brighter, but the head gets hot relatively quickly, so its really just bursts and then ramping down. i also used it with a powerex aa 2700 mah and it didn't seem much brighter than 2000 mah eneloop.
personally i like using the d11 around the house, kind of like a hand held saint minimus (which i also have) to a certain extent. i don't use it in the yard or outside though, prefering more throw for that.
i'm waiting for the sc51 in late oct, but i suspect i will be use it more than the d11. i think i'd prefer the shape of the sc51 to the shape of the h51 for handheld use, and the sc51 can also be put on a headband.