Just in terms of receiving ability, it's pretty close. Johnson is a bit bigger and taller and maybe a little faster in terms of top speed. In a game of inches, I think that givers Johnson the edge.
Stats are tough to compare, since there are so many team factors that go into that.
As far as who I'd want on my team, I'd definitely go with Johnson. I don't know much about Bryant but I am a Lions fan so watch Johnson every week. Aside from his receiving ability, he's everything you'd want in a player. He's durable, has excellent conditioning and is always working hard on (and off) the field. If he isn't in on the play, he still hustles, congratulates team-mates, helps guys off the turf, throws blocks, etc. And in a league that can be somewhat diva-ish, I've never seen him be anything but a gentleman. And I'm not saying none of that is true for Bryant, I am just not as familiar with him.