Hmmm... I think he has three really good one: Producers, Blazing Saddles and Young Frankenstein. After that High Anxiety had some good bits so did History of the World (eben though most of it isn't funny), Silent Movie wasn't that funny but had some good ideas... I think Spaceballs was almost up to scratch.
So... basically downhill after the first three mentioned (never seen 12 Chairs BTW) with Spaceballs as a positive exception.