The bottom line is that on talent Bryant is slightly better and both have incredible drive and that "special something". Bryant when he wants to be can be a better defender than Manu but Manu is also pretty darn good.
Manu on many teams could average 25 points per game although one wonders if he could take the pounding of being the go to guy every night.
However, if Bryant came with the same contract, even with my love for Manu and all the passion and energy he brings + Manu's own considerable skill one - I would sadly have to grab Bryant and ship Manu to the Lakers (where he would prosper). Duncan and Bryant potentially could be the best duo the NBA has ever seen as Duncan with his unselfish play and Shaq like interior dominance + defensive intensity would be unreal. Duncan + Bryant + Parker = no coach = could ever pass up that trio taking in the equation Bryant has expressed support for Popovich in the past.