Originally? Back in FFXI, so 2004-ish, it was my first MMO so party roles were a new concept to me. I started as WAR, I'd never been much of a magic user in past FF titles so chose the weapon wielder, as it turns out I was apparently pretty good at tanking and eventually became a PLD.
In regards to XIV I started a MRD in XI but ended up playing BRD throughout 1.0 until around 2.4/2.5 when I started tanking again, jumping between WAR and PLD. Now, I'm playing DRK and really enjoying it.