He's definitely the best receiving TE on the Jets, but he's not going to start over Baker because TEs have to block, too. Keller has been deficient in that area, thus far. For fantasy purposes, he's the better Jet TE to have, but he's going to be inconsistent because he won't be on the field all the time, and Favre will look for Baker and Bubba Franks at times, too. The situation is somewhat similar to Denver where Tony Scheffler is the TE to have, but Daniel Graham will continue to start over him because he's the better blocker.
Considering the dearth of options at TE out there, you have to jump on Keller for his potential alone.