They're all good, IMHO, but +1 on Summerteeth if you're exploring - they really found their groove on that one, before that they still tinkered with some country/rock vibes (which I love them doing, but some may find un-Wilco'ish nowadays). I also love A Ghost Is Born, but that might be a bit of an acquired taste - go for YHF before that.
There are also some side projects, like Mermaid Avenue 1 and 2 (with Billy Bragg), Loose Fur, etc.