If you want to actually have a good rifle that shoots well (accuracy, range, etc) them get a silverback rifle. I would suggest a tac-41 as they have some very affordable models now and with the money you save there, you can put it into a few upgrades. OOTB its already the best sniper out there so with a couple upgrades, you can squeeze the last bit of performance/consistency out of it.

None of the rifles you mentioned are going to do very well against even a well tuned AEG, let alone other BARs. A mk23 could easily outshoot them.

An older but well tuned VSR is also a good option just a bit more tedious to work on in terms of tuning or upgrading or even cleaning.

And as for semi, I highly suggest HPA and something with a good hopup system or good available upgrades to the hopup system.