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.