Lubitsch and Cukor are great directors, but like Vincente Minelli, their films aren't that much too my personal taste (at least compared to the others I mentioned). But I can see why they are so respected.
But I do like The Shop Around the Corner by Lubitsch. I respect how it was a comedy, but it had depth and he didn't dumb it down.
and Cukor did The Philadelphia Story, which is arguably the greatest ensemble comedy EVER. But I didn't like how he did his Tracy/Hepbuurn films (Pat and Mike & Adam's Rib) as much as the way Walter Lang handled them in Desk Set.
But honestly, they both made a lot of films I have never seen.
As for Wilder, not only was he a great director, but I saw an interview with him and he was so frank and funny about the way he did things I had a new found respect for him.
the thing i love about cukor and wilder is the same thing i love about hawks and the coens: the genre jumping. all 4 of these have made awesome noirs and awesome comedies as well as lots of other genres.
my favorite Cukor is The Marrying Kind (the concept and the judy make up for the aldo ray). And i actually like his tracy/hep's better than lang's or capra's.
As for Lubitsch, i think he's just the best. We have a big sign in our office that says "What would Lubitsch do?" I love the way he and Wilder can make such sexual movies that don't have any sex. Or even any kissing in some cases!