Coast V² or David 15

Can anyone tell me what's the difference between these lights, aside from the fact that one uses CR123 and the other AA? It'll also be good if anyone can recommend which of te 2 to get, im clueless.. and what about the Coast 1.25w Digitac? is it the same as the David 15?

Coast has hundreds of models,and with very little info,I got a coast 7740 AA battery ,1.25 w its very nice quality and a nice flood beam,Im happy with it.
I believe coast/david/eddie bower are all made by the same company.

Digitac I and Digitac II are the same as David 15 and 19 (not in order maybe).

The David series are a little on the low power side to have decent runtimes. They are not dim for the lower power consumption, just not driven to insane levels like some other lights, from a battery life prespective. I would hazard a guess that the 123 cell light might be brighter since the voltage is higher to start with. kind of like the light output boost when using a 3.7 volt lithium rechargeable in a QIII vs a standard lithium battery.

The only major knock on the Davids and several of the aluminum Coast/Led Lenser/Eddie Bauer aluminum lights besides weird batteries (in some) is that the contact parts of the bodies have to be kept clean or flicker occurs quite easily. The Stainless David series shouldn't have this problem.

I have a David 15 and 19 and like them despite the occasional flicker.

I don't have that particular light but I've got the 16 led/3C and it's built like a tank. Other than not being as bright as I'd like the only downside is that the thing is entire thing is completely smooth - slick almost.
They've got some really interesting looking lights but their prices are ridiculous! $80 for a three watt !? I don't think so. On the plus side their lights are built very well.