Probably an HK 91, or if I couldn't afford that (which I can't), a JLD PTR-91.
I am just very comfortable with the roller delayed blowback guns, and I am used to working on one (I own a CETME, which required a lot of work, and is very, very close to the HK91, just not quality wise).
I think it is a very durable, reliable and accurate system, and it's what I am most familiar with.
I.G.B.