See these in order.
A Shot in the Dark first, since it has nothing to do with "The Pink Panther" at all and it is probably by far Seller's best comedy work. The original Pink Panther is okay...a little meh, it's nowhere near as funny to me. Then check out "The Return of the Pink Panther", as it's probably priceless mostly for Catherine Schell's HILARIOUS and REAL crackups throughout the film that Blake Edwards decided to keep in, then finish up with "The Pink Panther Strikes Again", one more effort that prides itself on slapstick. To me, the moat scene alone is sheer comedic brilliance.