As an in-ring performer? Without a shadow of a doubt. My top 5 in ring performers of the last 25 years (in no particular order) are: Hart, Flair, Savage, HBK, and probably Angle, mostly because he brought such intensity and believability to his matches. Still, I'm leaving off Steamboat, Sting, Bulldog, Perfect, Owen, HHH, Jericho, Malenko, Misterio (WCW days), Eddie, Benoit, Edge, etc. That top 5 alone is impossible to really rank. If I add personal bias to the list alone, Eddie would probably have to beat out someone for a top 5 spot (sadly, probably Savage).
Now, if we're talking about an overall package, then no way in Hell is Hart a top 5. Top ten if I were really giving him a lot of credit, but never top 5. In Attitude Era WWF alone, he would have to compete with HBK, Rock, Austin, HHH, Foley, and Undertaker. I don't think Hart was a more complete package than even Foley was. It all amounts to the two most obvious flaws in him: he couldn't tell a story on the mic and his television personality was just boring. That's why when wrestling moved towards an edgier market, Hart was left in the dust; he had zero edge. Bret was just boring. Period. I liked Bret well enough back in the day, but I never loved him because he didn't do anything to make you love him. It's the same for Cena; he's clean cut, he does everything well, but there was never really any, "wow factor," to him. Like I've said a million times, Cena to me is like the watered-down love child of Hogan and Hart. You take Hogan's wrestling ability, or lack there of, mix it was Hart's personality, or lack there of, and you have Cena. He's a marketing machine. Kids don't care about actual wrestling, and their parents want them to cheer for the squeaky clean, lily white, generic hero. Cena at least had a little edge to him when he did the rapper gimmick, as dumb and painful as it was, but that's long gone. I've seen so many people say that Cena will eventually turn heel in a big way like Hogan and he'll reinvent himself. No he won't; he's going to just fade into the rest of the pack like Hart did until he retired.
So, besides my little Cena rant, that's how I feel about Bret. The man was one of the single greatest in-ring performers IMO, but the buck stops there as a total package.