I have an X2, which is a two CR123 xenon incandescent. It's a nicely made light, and I like the chalkboard-type finish of their hard anodizing. But I find the pentagon-shaped "nut" on the bezel and tailcap to be ridiculous. It's more for looks than function. Surefire at least puts a hex-head on theirs, which is more wrench-friendly. (Yeah, you probably won't need to wrench your light open, but when THE TYRANNY comes, your light needs to be as serviceable as possible.)
Also, the springs on the lamp assembly aren't ground flat on the ends like Surefire; the flat-ground springs will make superior electrical contact. But the PentagonLights have gold-plated springs; I don't know how their corrosion resistance compares to Surefire's springs, but it's a nice touch.
For the $$$$ I would probably take a Surefire E2e over a PentagonLight X2. The X2 has a Type III (hard ano) finish, where it's Surefire competitor size-for-size, the 6P, has Type II (sulfuric) anodized finish, which isn't as tough. The E2e is smaller than either, but has the hard ano and parts are more readily available than PentagonLight.
Having said that, I think a PentagonLight is a very worthy addition to a flashlight collection. But if you have to have only ONE light, I'd go with Surefire.