Of the ones I have played:
What I like with FATE is that characters are relatively competent from the start, and it is made for a it more cinematic feel, where it is a pulpy larger-than-life feel.
GURPS is best if you want fine granularity and a kind of realism in the game. It is very fiddly though. But on the other hand the sourcebooks are vey well written and lots of people use them as source material for other games.
I have only read Savage Worlds, but I do not like the way they handle stats with different dice
So, I'd like to use this to make a point - Each so-called "generic" system still has its own style, and lends a different flavor to the play experience. Both GURPS and Fate can be used to do "fantasy", but they will not be the same in play, by a long shot.
I love Fate for its pulpy-action feel, and how character action really comes down to
who the character is. If you are looking for a flavorful, fast paced play experience that yields a fun narrative, in which the characters interact with the situation you've set up, Fate is awesome. However, if you want a deeply tactical game... Fate probably isn't appropriate.
I have to agree that GURPS, does gritty/"realistic" games pretty well, and the rules are quite detailed - and yeah, the rules can get fiddly, which to some people is a feature, not a bug.
Savage Worlds is, imo, a pretty decent example of a traditional game design made into a "generic" core ruleset. Not rules light, not rules heavy, not particularly narrative driven. If I wanted to play D&D, but didn't want to use the d20 ruleset, I'd probably choose Savage Worlds.
Cortex Prime is more of a toolbox than a game you'd play directly. You assemble the bits you want. That makes it a bit difficult to say how it works in play, because it depends on what bits you choose. In my experience it has been very good at media genre emulation - The Marvel Super Heroic Roleplaying game, Leverage, and Tales of Xadia games have all been quite fun to play.
Cypher System I own, but I haven't used a whole lot, so I'm hesitant to try to characterize it.