I actually never liked any of the Wilder/Pryor collaborations...but individually (at least when they were in their prime) they were both hilarious.
Both Pryor and Wilder could be guilty of shameless mugging and face-pulling, and I felt that they over-indulged themselves in this regard on most these movies.
Pryor was the worst offender, and indeed overacted and fooled around endlessly in his later movies. But I always put this down to him being tied to a script which was not as funny as it should have been, so he always felt the need to jazz it up by pulling stupid faces. But then again, as improvisational stand-up comedy was his real forte, tying a man like that down to a script was always going to be problematic.
And though Wilder was known for his occasional moments of manic comedy, such as in The Producers and Young Frankenstein, he was actually a very subtle comedy actor. His performance as the doctor who falls in love with a sheep in Woody Allen's Everything You've Always Wanted to Know About Sex was a great example of this.
And for me Pryor's best screen performance is as a Detroit car worker in the film Blue Collar. He was given free reign to improvise his dialogue, and he gives a very believable and naturalistic performance. It's a serious movie, but it does have some very black humour.