currently pelt3 > squire3 > murmillo
I reached at least 180 STR then rest to CON (which by level 330, around 190). The reason for this is that in later dungeons, you need a decent amount of damage to help your party kill faster. Investing in full CON is nice if you can compensate your damage with gear but if not, STR helps. Also, my HP is hitting around 70k with just 190 CON.
But if you are after block rate then yeah, a higher CON will always be better.