I have an ICS 551 and I've been very happy with it. For $260 you can't beat the value for your money with any other sig out there. It performs well out of the box and is internally easily upgradable.
Only issue is mags, if you want midcaps you'll have to do minor modification to fit them but it's easy and only takes a few minutes a mag with a file.
http://www.airsoftcanada.com/showthread.php?t=117937