Most people would probably say "Now You See Him" or "Try And Catch Me", which are excellent choices indeed.
But I'd also recommend "Suitable For Framing" and "Murder By The Book".
The thing is, there are lots of top-notch Columbo movies, which results in a higher probability of him really liking the movie you'll eventually choose.
I would recommend "Negative Reaction." A lot of good clues, good tension between Columbo and the murderer, and that unforgettable cemetery scene which helps to define Columbo's character.
Agreed..."Negative Reaction". Has it all, great chemistry, just enough humor (not too much),
Columbo is
"modest and mildly eccentric" to the right
degree, a really clever set-up by Galesko making
the case seem uncrackable,
great acting by the victim (who often ends
up as a cipher in the different stories)
Antoinette Bower ("what is this Paul, some
newly found masculinity?") and great directing
and camera work. A "10"!