First of all, the success of there respective careers has absolutely nothing to do with who is better. This is not a competitive sport....Mcmahon largely decides who succeeds and who fails, and his judgments don't seem to be based on in-ring skill very often. If you believe that high profile matches and title reigns indicate who's 'better', than you believe that the Ultimate Warrior was better than Ted Debiase, that Hulk Hogan was better than Ricky Steamboat, that Kevin Nash was better than Dean Malenko, etc etc etc. Hence all of the 'well who headlined Wrestlemania?' arguments are invalid.
Second, our view of what's more exciting and what's more engaging in the ring has a LOT to do with crowd reaction, which has a LOT to do with who is pushed. Give the Goldberg/Samoa Joe push to anyone on the roster and they will get over...give them a stale character and job them out and they will go nowhere. Look at Lance Storm, William Regal, Evan Bourne, or Malenko to name a few. They have/had mad skills, but didn't have the promotions creative machine behind them. Whereas Edge has had the creative machine behind him 100% of the way...his push continued through some terrible face runs and he was repackaged and repackaged until something stuck (the Rated R Superstar). If you don't believe that a performers gimmick and push can influence the crowds reaction to there in-ring work, than you are in denial about the existence of Hulk Hogan. (This is not to say that you don't need personality or talent to get over....but that you need both personality/talent and a push).
That being said...(and totally my opinion)...
Christian is technically sound, theres no doubt. The moves that he does are done right, and he very rarely screws up. But I'll agree with some other posters that theres a certain 'flashiness' missing from his in-ring work and move-set that we've come to expect, and I've often felt that his move-set doesen't reflect his physique or personality very well (the Unprettier/Killswitch is completely unbelievable against a larger opponent, for example. Although I will say I think that his style has improved a lot since arriving in ECW). Edge's is much more explosive and he seems to put a lot more emotion into his matches, which conveys well to a live audience. On the other hand, Christian has shown an ability to carry just about anyone to a good match, which I don't believe Edge has. Edge's matches are also a lot more predictable than Christian's (I doubt this is Edge's fault though. It seems common for main eventers in WWE). In any case, at the moment I'd have to say that Christian is the better technical wrestler, while Edge is the better in-ring performer and entertainer, although again I don't know how much of that has to do with their relative position's and directions within the company. That's the thing really....you can't make a fair comparison until they are both in the same position. In regards to that...
Christian has accomplished a hell of a lot in his career without WWE's creative 100% behind him, certainly more than Jericho or Edge before they received there main event pushes (he's carried two companies...). And sometimes it can take a while for the WWE to get behind a performer. Jericho, Jeff Hardy, Benoit, Eddie, etc...a lot of guys have been in Christian's position and have eventualy gone on to superstardom. So Christian's time may yet come....and probably will. WWE will likely give him a major title run to keep him happy and prevent him from jumping back to TNA when his contract expires (assuming it still exists). When that happens, we will see if Christian can become as big of an overall asset as Edge currently is.