Is fighter X better than fighter Y?

This is the kind of question that gets discussed all the time, but doesn't really have an answer.
First, best for what? Every fighter is designed with a particular set of requirements in mind. "Fighter" is a fairly general term that covers a multitude of missions. A Tornado F.3 or a MiG-31 is an excellent long-range interceptor, but you wouldn't want to send one of them up against an F-16 or an Su-27 in a dogfight.
Second, the aircraft itself isn't the only factor involved, or even the most important one. Put two aircraft of similar (or even somewhat different) capabilities up against each other, and by far the most important factor is the relative skills of the two pilots. It's widely believed that superior pilot training was the main reason why American F-86 Sabres consistently gained air superiority over technically superior Russian MiG-15s in the Korean War.
Third, even apparently identical fighters can differ enormously in their electronics fit; and in modern fighters, the electronics is at least as important (not to mention expensive) as the airframe. Export versions of fighters are normally much less capable in the electronic sphere than the equivalent models for the home air force, even when the aircraft have the same designation; does anyone expect the F-16Cs exported to, say, Egypt to be anywhere near the capability of the F-16Cs in USAF service? Older aircraft can be upgraded to modern electronic standards at a fraction of the cost of new fighters, an option increasingly popular in these days of tightened defence budgets (for example, the RNZAF recently upgraded its Skyhawk fleet with a radar and avionics suite equivalent to that of the F-16A).
Most of the modern generation of fighters are fairly similar in performance. Leaving out specialised interceptors such as the Tornado and MiG-31 mentioned above, if almost any two modern fighters came up against each other in a dogfight, pilot skill would certainly be the main deciding factor. We can (and certainly will) argue endlessly about the relative merits of, say, F-16 vs Sea Harrier, or F-22 vs Su-35 (both the subject of recent discussion on this newsgroup; Harriers versus conventional fighters is a particularly hardy perennial), and there are real differences there; but such technical details are not the most important thing in combat.