What's the difference between an L2 Aviator and the Aviator Brenner? (On the messer forum)

I'm also assuming that if I'm going to pay $150 for a flashlight from Surefire, I should just go with one of their LED models?

Also, what are some of the differentiating factors between an A2 and an L4?

Thanks so much... sorry for the newbish questions.