If you're trying to decide between an ICS Cansoft M4 and a G&G Cansoft M4, try searching some reviews here to decide which one you wait. From what I have heard though, the ICS Plastic is much shittier, so unless you plan to get a metal body or a new body for that matter, I'd get the G&G. Internally they are a little bit the same, but the ICS M4 takedown is much simpler.. (I have a full metal ICS and it's awesome. the takedown is nice.. google it)..
Read reviews on both guns, decide which one you want more. The ICS Cansofts seem to be of cheaper quality than the G&G Cansofts (full metal guns are different from what i understand, the ICS and G&G metal counterparts are much higher quality (even internally a littler bit better))
Sorry for all the brackets.. there's a ton of differences but they are pretty close performers. The G&G's magwell is not as tight as the ICS's though too, as in the mags will be loose and you need to tape them up. The plastic is MUCH higher quality though.