I ran a quick summary of RMSS skill categories: Ag appears 30 times in the list of categories. This is followed by In (16), St (15), Me (11), and Re (10). The remaining five stats all appear 7 times or fewer, each. Of course, many of the St/Ag occurrences are weapon/MA based so, I would say that Ag/In/Me/Re are the most important stats for skills.