I said this a few weeks ago, but Lendl's clay court credentials are incredibly underrated. Over the years I've seen people ranking the likes of Kuerten, Federer, Vilas and Muster above him on clay, which is absolutely absurd. None of those 4 players compare to him on the surface.
It's close between Lendl and Wilander on clay, but I would go with Lendl as his overall clay court CV is slightly better, and in my opinion his peak standard of play on surface was better than Wilander's. Wilander himself has admitted that as well.