First, let's look at the free agent or trade options for the Jets. The best free agent quarterbacks are Jake Locker, Brian Hoyer, and Mark Sanchez. I don't think any of those guys would be an upgrade over Smith, and it would cost the Jets a lot more money. On the trade front, the only guys who could be dealt are possibly Kirk Cousins, Robert Griffin III, or Jay Cutler. The last two would be eaten alive by the New York media, and the first one just flat out stinks.
Now take a look at the draft. This draft class has two quarterbacks who are "first rounders", but neither will be a Jet. Marcus Mariota from Oregon will be long gone when the Jets pick at six. Jameis Winston out of Florida State could be there at six, but would make zero sense for the Jets. He has talent, but has to many off the field questions to be successful in New York. After those two, the class is so weak at the position.
With the right offensive coordinator and a good offseason rebuilding the offensive line and adding some weapons, Geno could succeed next season under a new coach. As much as fans want an upgrade, Geno Smith is the best option for the Jets in 2015.