I own both.
What everyone else said is true.
The 4AA, 7LED will fit into your pocket easier, is lighter, puts out a lot of nice light.
The 3C, 10 LED puts out even more light, is a little heavier, a little bigger, and will probably run for a longer time, and appears to be better built, with a large heat sink on the LED's (that should not matter, Streamlight has a lifetime warrantee on both, should they break).
So, it's 5
m, you are going out hiking and don't know if you will make it back before dark, you grab the 4AA and slip it into your pocket.
It's 9:30, and you have to go out in the wilderness for 2 hours, you grab the 3C.