I'd say Dogma was Smith's last great film, with Zack + Miri, and Clerks II being the best of the bunch succeeding it.
From a technical standpoint, Chasing Amy may have been his masterwork. He really found the perfect blend of his crude humor, and emotions with that one. The film hits your heart strings deeper than Mallrats, or Clerks ever dared to; which can also be partially attributed to his growth as a director at that point. I don't think Smith would have ever gotten the budget to make a flashy film like Dogma, had he not struck gold with the hilarious and heartfelt Chasing Amy first.
Clerks is the one I watch most though. Randal Graves is one of my favorite film characters of all time, and Jay + Silent Bob work great when presented in their most rudimentary nature. The film's so raw, it almost reminds me of a slacker comedy Eraserhead or something. Which makes sense since Kevin talks about being very into Lynch at the time. The original cut where Dante gets shot at the end leaves the film ending on a much different tone. I love the use of title cards too.
I hated Cop Out. I don't think anybody really liked it all-too much. There's a reason he went back to writing his own shit immediately after.
If you haven't seen it yet, and want to check out an insanely cool Kevin Smith related film, I highly recommend Bryan Johnson's Vulgar.
It's an extremely dark comedy starring Brian O'Halloran (Clerks) as Will, a down-on-his-luck party clown who... well, I don't want to ruin anything for you. Like From Dusk Till Dawn, or The Crying Game... the less you know, the better. Just hunt it down somehow, it's a masterpiece. Kevin makes a sweet beardless cameo too.
But yeah... I'm down with Kevin Smith 4 realziez.