Hi Fuzz
Can I ask if you have any Surefires already? Just so we can suggest some better 'lego' solutions based on what you already have.
I've got a number of Surefires in the category you're looking for including the G2, G2z, 6p, M3, 9p and M6.
Some Questions:
1. Are you intending to purchase only one Surefire, or are you likely to 'get the bug' and get more Surefires later on? For example if you get an L6, a M6 and an A19 body extender (with the correct lamp assemblies) You would have a L6, M3T, M4, M6 as well as being able to put the KL6 led on any combination of those bodies.
2. Do you intend to carry it e.g. pocket or holster or is it a car / house / bedside / WOW! light?
3. Do you like plastic or metal? If you don't really mind, the nitrolon body is more durable than metal to both shock and being scratched (not to mention being less likely to scratch other items). It also goes better in the cold.
Something else to add in is that you do know that you can put a P61 lamp in the G2 to make it put out 120 lumens, but it will only run for about 20 minutes. Conversely in the C3 the high output P91 also puts out 200 lumens. Both are Surefire products.
I only ever put the high output lamps in my Surefires, I bought mine to be the brightest! You do notice a difference in brightness between 120 lumens in a G2 and 200 lumens (in my 9p - same lamp as the high output in the C3).
Between the G2 and C3 I would buy the G2 (make sure it is the new LOTC version) hands down because of its size, durability, and you can normally find them at great places on the buy and sell section of these forums. Pick up a P61 and instant pocket rocket!
The reason I got the 9p and the G2 is that my M3 (and the C3 is similar) is not as 'pocketable' as the other two. Mind you that was only my excuse, my pocket light is my L4
My logic is two is one, one is none. I'd get a G2: later on you can look at getting a C3, an A19 and turbohead for the g2, or go for the millennium series.
I haven't seen the turbohead on the G2, but according to opinions i've read you are better off getting the turbohead in a 3 cell or more configuration to see any substantial differences over the plain G2.
Either way the G2 can always be put in the car or on the bedside if you get something else later on
Just my 2 cents based on the information so far