Having worked through most of the David Suchet Poirot mysteries he had, my dad turned to the other tv movie versions of Agatha Christie's work, which including a few stories with Peter Ustinov in the Poirot role. Which was different, since Ustinov doesn't play Hercule Poirot as nearly fastidiously neat as Suchet does. He's also much more abrasive and frustrated with his sidekick Hastings. Suchet had a sort of amusement at Hastings' frequent befuddlement, but it was good-natured. Ustinov is more mean-spirited about it.
The one I found most interesting was Thirteen for Dinner, where Ustinov plays Poirot, and Suchet plays Poirot's other sometimes partner, Scotland Yard's Inspector Japp. What was curious was the interactions between the two characters were more like Holmes and Lestrade, with Poirot bugging the hell out of Japp, and the inspector resenting the interference of this civilian in his investigation.
Not that Japp didn't have a point. During Poirot's big speech revealing who did it and how, he also reveals that he found a critical piece of evidence in one of the victims' possessions, a piece of evidence he failed to mention to Japp until that precise moment. Which sounds like withholding evidence, but Poirot was right, so I guess that makes it OK.
It does bring up a problem I have with a lot of these sort of mysteries. You have this indepenent investigator nosing around, and they find some crucial piece of evidence during their attempt at breaking and entering. Then they present it as the clincher to prove their theory that so and so is guilty of murder. We know they did find it exactly where they say they did, but a lot of times there wasn't any one in the story there to witness it. The rest of the characters only have their word for it, which would seem to be a potential flaw in prosecuting the case. I mean, that's kind of an unstable chain of evidence, but most of the stories are concerned with finding the killer, and prosecution is handled off-screen afterward.