I'd rank them;
1. Keller
2. Stevens
3. Lee
Keller is the most talented of the group and I think he has the highest upside. He not only has talent but he has a QB in Favre who has a proven history of throwing to his TEs - especially in the Red Zone. I know the Jets were in passing mode for much of last night's game, but Keller got a lot of looks in the Red Zone. I think that bodes well for him going forward.
Stevens is who he is. I don't think he changes much at this point. He'll have some good games like he did in Week 3 but I don't trust Griese to help him get points consistently. I do like him this week against the Packers. Green Bay has had issues stopping TEs dating back to last season.
Lee doesn't seem to be as involved with Favre gone. The Packers are using more 3- and 4-WR sets and that keeps Lee out of the mix. He's pretty much a guy who gets 2-3 catches a week, 30-40 yards and that's it. TDs may be tough to come by for him this season.
On a sidenote, the talent at TE really stinks this year. If you don't have one of the few top-level TEs (Witten, Winslow, Gates, Gonzo, Cooley and I'd include Owens - Shockey and Clark would be there when healthy), you're stuck playing the matchups each week.