My favorite is “Condo made of stona”.
His first movie is still incredibly funny if a bit crude (at least by 1970s standards). The Jerk. Definitely worth a rewatch if you haven’t seen if for a while.
Only other one worth a watch is Planes Trains and Automobiles where he’s more the straight playing off of John Candy.
Avoid Sgt Bilko and Dead Men Don’t Wear Plaid with malice.