Ok heres my $.002 on the issue. Both have the same light engine to them, as well, unlike the difference beteen the standard 6p and g2, the 6pl and g2l have the same head on them, the bodies and tail wsitches are what is different.
I have actually bought these for a couple of Law enforcement (RCMP) friends of mine, and hey commented on a few things.
1. The G2L does not get as cold on the hand as the Alluminim 6PL (in Canadian winters even with gloves your hands freeze with the metal 6
2. They find the G2L to have a more glove friendly grip, although if you are using it in hand only the 6PL might be better as the 6P grip is fantastic.
3. Blood/urine/excrement/vomit/mud etc seems to clean off better the plastic bodied G2L than the 6PL. Although if you run the 6PL body under hot water it should come off ok. but most times my friends just use hand sanitizer for their hands and a drinking bottle of water for the light. If you in the field and u only have a water bottle, maybe the G2L.
4. The 6PL and G2L both come with the momentary on-twist on/off tailcap, but if you want to go to a clickie (on/off only click) style of tailcap, your lmited with the plastic end on the G2L. You can still use one, but then you have a quirky looking half plastic half metal light, and may as well have gone with the 6Pl.
I personally have used both lights and find they are both great for different reasons. The 6PL even in its stock form feels quite substantial and quality. You feel you are using a precision piecw of equipment. If you are not faced with extreme cold and mainly use hands etc, the 6PL is great. On the other hand, the G2L does offer great comfort in gloves, will not get nearly as cold, and i find easier to hold and activate i slippery conditions. Plus the cleanup on the thing is much more easily achieved in the field if you want to just 'water-bottle' the light down.
Both work well, for different purposes. Chek out the weight too on these lights because there is a diffence and if weight is of concern, then try the G2L. You can actually hold the light in your mouth if you need to (being plasic) and not have it too heavy. That wont work with the 6PL.
And although you dsaid you didnt want an opinion on another light, maybe check out the 'backup' by surefire (its off their website now but you can find plemnty of threads on here). It looks like a great light.
Dano