Slovak and Moravian are pretty much close. But it is hard to compare literary Slovak with Moravian dialects, as there is no codified literary Moravian.
So it depends which Slovak dialects and which Moravian dialects you compare, then. Some are quite distant, without much mutual intelligibility.

Czech has no real dialects, they were assimilated. Although some areas still show some special features. Moravian dialects are similar to Czech language, and most of them are also very bohemized now (czechified).

Slovak literary language is similar to Czech but the degree of mutual intelligibility is not really high unless there is an exposition (now proven by some Czech children born after the dissolution of Czechoslovakia who had almost no exposure to the currently used Slovak literary language and they have serious problems with understanding).

Then there are differences between various dialects of Slovak. There are actually two levels of dialects:
1. various original historic dialects or languages (about 30 or 40),
2. various "dialects" of spoken informal standard (not many I suppose), which are composed of literary language + influences from local dialects + Czech influences + local slang.