Flying against the MiG-21 and MiG-23 with the F-15 was relatively easy. The Fishbed is difficult to see and you have to ask yourself if that speck on the canopy is a piece of fly do-do or a MiG-21? I also flew against those airplanes while flying the F-5. The MiG-23 was still a baby seal while the MiG-21 was much more evenly matched.
I have flown against the MiG-29 and Su-27 while flying the F-16 (Blocks 30, 40 and 50). Since I have 500 hours in the MiG-29, I'll talk a little more about it.
The Fulcrum is a very reliable airplane. It seldom breaks. The same can be said about the F-16. The F-16 absolutely owns the MiG-29 from beyond visual range (BVR). Initial contact ranges from both aircraft are similar although I'd give a slight edge to the F-16. The BVR AMRAAM against the AA-10A is a joke. By the time the Fulcrum pilot gets in range to shoot an AA-10, the AMRAAM has gone active and the F-16 pilot has turned around and is going away. If forced to merge, I'd still give the advantage to the F-16 pilot. His sensors will tell him exactly where multiple MiG-29s are. The Fulcrum pilot may have situational awareness (SA) on one F-16 and his displays won't point out exactly where his F-16 adversary is. If the MiG-29 pilot does have SA, then his helmet-mounted sight and AA-11 Archer make him a deadly adversary. If the F-16 pilot has the Joint Helmet-Mounted Cueing System and AIM-9X, the advantage is still with the Viper pilot as the off-boresight capability of the AIM-9X is significantly higher than the AA-11. If it comes down to a gun fight, I still give the advantage to the F-16. The F-16 sustains a high-g turn better than the MiG-29, has better outside visibility, is more responsive and easier to fly, rolls significantly faster and will out accelerate the MiG-29 like the Fulcrum was glued to the floor. The Fulcrum is a very sloppy-flying airplane. I'm not saying the Fulcrum is a push over; the Viper pilot needs to bring his A-game. The Fulcrum pilot better prosecute the merge pretty fast because he doesn't have the fuel to hang around very long.
While flying the MiG-29, I have flown against the F-4, F-14, F-15, F-16, F-18, Tornado F-3, and Mirage 2000. The 'deadliest' was the F-15C, the worst was the Mirage 2000. It was the only one I'd walk out the door knowing we were going to kick their asses.
While flying the F-16, I found the Su-27 to be a much more lethal BVR airplane with the exended-range AA-10C. The Flanker also has a very robust infrared search-and-track system that can also cause issues. You still have an advantage with the AMRAAM. You just have to be more cautious. In the visual fight, the Flanker is still impressive for an aircraft of its size. If the Su-27 is fairly heavyweight then it's a wallowing pig. If it has burned off some fuel, its nose-pointing ability a high angles of attack is impressive. So is its energy bleed off. If you can get him to give up some energy, I found it very beatable with the F-16. On the other hand, the Flanker is a lot like the F-15 - it's a maintenance nightmare.