I would chose ICS followed by Classic Army.
If your on a budget, I would buy an M4 by ICS, it s affordable, looks good and is very reliable, fires 365 fps out of the box. Later on, you can upgrade it by buying a 100$ part that lets you change fps back and forth in a few minutes. Its easy to change the spring to 350 fps if you play cqb. Runs all day on a 9.6v battery and comes with a charger. Compatible with almost every brand of magazine.
Only down side with an ICS is that you cant change the gearbox for another brand, you have to stick with ICS.