For Chairsofting and collecting, Id suggest you can go with the nice Vipertech GBBRs if you can get your hands on those for realism. they're prob one of the nicest GBBRs in terms of realism.
THen of course if you're planning to skirm and game Then I'd go Marui MWS or GHK.
At the end of the day it all depends on how much moolah you wana spend and how deep of a hole you wana go