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I've watched a fair few Landis movies (most of the ones you've mentioned - not Coming to America, though it is on my to-do list - plus Animal House, Into the Night, Three Amigos, Beverly Hills Cop III, and Blues Brothers 2000) and, aside from The Blues Brothers (and, to a lesser extent, American Werewolf), none of them have ever really worked for me. Most of them are middling, some of them are downright bad. When I think of directors where I only really like one movie they've done, he's obviously the first one I think of.
Smith, on the other hand...I used to like Mallrats but think it's aged rather badly now, have never truly liked Chasing Amy (though it's significantly better than Mallrats), like Dogma well enough but never feel the need to rewatch it, revisited Jay and SIlent Bob Strike Back a while ago and that's also aged poorly, Jersey Girl is an extremely passable step out of his comfort zone, Clerks II was a fun enough retreat into the comfort zone that's about on par with Dogma for me, Zack and Miri Make A Porno is awful, Cop Out is about the same, Red State is a somewhat decent little horror that I doubt I'll ever revisit, Tusk was atrocious and my least favourite of his films (and in contention for one of my least favourite films ever), and Yoga Hosers...well, the best thing I can say about it is that it's not Tusk. I have been meaning to watch the Evening with Kevin Smith DVDs (picked them up cheap a while back), but considering my feelings about his actual films I can't quite muster the enthusiasm to watch four to eight hours of him just talking.
(while I'm talking about my choices, I picked Cox because Sid and Nancy is just okay and I even put Straight to Hell and Walker on my all-time worst movies list a long time ago, though I obviously don't consider that list to be very current and thus I really want to revisit them to see if they're just things I just didn't get at the time - who knows how I'd feel about any of the film he's done since then, though)
(as for Robinson, well, it doesn't help that he's only directed four movies - aside from the all-time fave of Withnail, there's the significantly lesser - but still somewhat watchable - How to Get Ahead in Advertising and the extremely dull adaptation of Hunter S. Thompson's The Rum Diary. I did pick up a cheap DVD of Jennifer 8 for the completionism's sake but it just looks like such a generic '90s Hollywood detective thriller that I may never get around it)