Jim's. Service is only tolerable but sandwiches are excellent.
Marshman is right, though.
I more often get a sandwich from the guy running the deli downstairs because I know him, he makes great stuff and he's so conveniently located. As for Pat's the sandwiches are good but I have only had very rude and obnoxious service there. I've heard worse about Geno's and so have never gone there.