"In which context? In any technical context they are both bad because they're ambiguous (as are year abbreviations YY) and this is the big problem with Americans using the abbreviation in technical contexts and why we have an ISO standard (of course, not without its own problems). Outside of a technical context then you might as well write out the month name or three letter abbreviation. MAR-14 or 14/MAR or whetever."
Back when I worked a tech pubs job where I had to co-ordinate our materials with our branches in the UK and Australia, I got in the habit of denoting the month in Roman numerals. Still do it to this day for most purposes. I'm mostly out of that field these days, so I don't know if it's still done but it used to be quite common in scientific publications.