Well, as others have noted, these two lights are VERY different beasts. And which one you ought to choose would totally depend on what your intended use(s) is/are. To me, it's not even something that should stoop to the level of Fenix vs. SureFire, because the two lights aren't even functionally comparable (like comparing apples and oranges).
Anyway, I'd say the G2L is a light that I would throw in my toolbox, or stash somewhere in the house for emergency purposes, or use as a car light, etc. For me, for example, it has replaced my use of the Mag 3D (except in cases where I actually want a huge club, or where I need the extra throw). The G2L is not, however, a comfortable one to have in your pocket all the time. Also, the Nitrolon body could be much more pleasant if you think you'll have to use the light frequently in the cold.
The L2D is definitely a much more pocketable light. This is the one that I would choose if I were looking for a light to carry on my person on a daily basis. Since it takes AA's, and since most AA's that one would have access to are alkalines, it's not a light that I would want to store as an emergency light, car light, etc., where you never know what extreme temperatures it might have to be used in, or where it would go for very long periods with no use. But of course, if you're using it everyday, and thus likely changing out the batteries on a somewhat regular basis, then its use of AA's could certainly be an advantage. Of course, perhaps the biggest plus to the L2D is that it has multiple modes, so for most EDC purposes, I'd say that's a huge advantage over the G2L.
Bottom line: consider what you intend to use the light for. I trust CR123 lights a lot more than I trust AA ones, but that's because I don't necessarily know how long my cells will sit around before I use them, and I've had infrequently-used AA lights that pooped out on me at times when it would have been really handy to have a light. But that really depends on your own use of the light and cells.
Of course, you could do the good flashaholic thing and get both. After all, it never hurts to have backup.
