May, no contest.
MCC was a very good batsman but he was a beneficiary of having most of his career in the 1960s, not the 1950s. Wickets massively laxed down in the 1960s, especially overseas, while in the 1950s England and Australia were some of the most liveliest, spicy wickets in the history of the sport. The batting average in May's games in England is 24, referencially the batting average for Kohli's games in South Africa is 23, for Cowdrey's games in England it's 28. For May in Australia it's 25, for Cowdrey 31. May is miles better than Cowdrey in England and imo better in Australia, Cowdrey is better in West Indies though May was ill in 1960, and definitely better in South Africa. Overall, it's obviously May, one of the greatest home batsmen of all time when context of the wickets is taken into account.
Michael was better than Greenidge and Gower, though.