I kind of thought vice versa to Yellow's statement. Landorus-I = banned, Kelds = Stay
I find Landorus more threatening since it can bluff the special set with U-Turn > Rock Polih(although less threatening). You need to find out which set is using, to use the apprioate counters. Since it can use U-Turn w/ EBelt and it's the special variant, what you thought was a counter, isn't really.
Keldeo in the other other hand, far easier to handle, IMO. It is usually Choiced, SubCM, and Offensive CM(and I guess EBelt?). You just need to figure out what's the item and figure out the set.