I can probably give a good answer on this one, I have seen both play over 10 games live as I seen Crosby play about 40 times live and Spezza about 25 games live and on TV.
Crosby IMO has the better offensive talent and all-around game, as for comparing this is how I would do it.
Spezza has alot of offensive tools that will make him a superstar though I found Spezza does lack one thing, he tries too much with the puck and he looks for the pretty play every time. Crosby on the other hand controls the tempo of the game and the players start to play his game, he uses his linemates well in getting the puck down the ice, though he is capable of deeking the other players out he sticks to the safer plays. Shooting wise they are both great very accurate shooters with a good shot. Crosby's IQ of the game is unmatched in players that I have seen play, this is something Spezza does not have as good as Crosby. Though both are great on offense, Crosby IMO has a way higher upside with offensive output, but to go along with this Crosby also plays tough and great two way hockey. Both are great with the media.
The two IMO are not comparable in game styles, one is a run and gun player who loves to show boat but has extreme offensive talent (I am a Spezza fan by the way), and the other knows how to take over a game with smarts and unmatched skill. Crosby is being hyped 5 times more than what Spezza was and it will only get worse IMO.
