I think the best pick would be a Mig-23, because with the R23 , the HUD and the better Radar, it would have a better chance against 4th gen fighters. The armament of the Su-22 is even more limited compared to the Mig-21bis. It can only carry R60s (wich should be patched soon) and R3S (maybe R13M1). I think a good pilot, who has a lot of Mig-21 expierience can ruin the day of a lot of F-15 Pilots at the moment.