Most of the catalog is pretty strong except I didn't really like that stint when they were a full band (To All My Friends & Family Sign) & most of their debut album (Overcast) has a pretty dated sound overall (still worth a spin tho). Other than that their albums range from good to great & all are worth checking out.
You Can't Imagine How Much Fun We're Having is probably the best produced overall, & Lucy Ford is probably Slug's best lyrically if you want to start with either of those. examples:
YCIHFWH
Lucy Ford
Also make sure you check Felt 2, the Sad Clown series & EPs/mixtapes
And they have a ton of unreleased stuff/collaborations/guest spots that's as good as their best album tracks.