It depends. If you are buying the Cansoft version, get a G&G. Their polycarbonate lowers are just a tad bit stronger than ICS's. If you are getting access to the classifieds why not consider Classic Army. Like G&G, their standard V2 mechbox will be a little bit cheaper to upgrade (it's not a HUGE difference, I own an ICS and it's not that bad..). They come with some of the most rock solid internals and stellar looking externals this side of the 600 dollar zone. Full metal G&G's come around a little bit less, but are out there. They're similar in price, but most people will tell you to go for the CA. If you manage to find a full metal ICS (there are a couple around, less common then even a G&G fullmetal) they are OK, just make sure you get the one with the Black body. The grey body are version 1 and upgrade 1 (ics version, still split v2 mechbox) both come with a crappy switch, nylon bushings, a shotty safety and the infamous Turbo 2000. The V2 ICS M4's have a better switch, copper bushings, an improved strength safety and the Turbo 3000 (which is actually a GREAT motor.)
I personally have an ICS and am a bit impartial to them, although mines been PLAGUED with problems. I still prefer them, they're nice. But stay away from the cansoft ones, they have a tendency to break.
Hope this helps!
EDIT: I have no experience with the dark tinted ICS lowers vlad is selling. I've only heard of the clear ones breaking (007 and mach1 sold them)