I gotta support what others have said and say that PLD is probably the easiest overall.

The healers are all about equal in my eyes. Some fights differ, where the WHM will be really on their toes but a SCH or AST might not be so busy. Likewise, some fights a SCH will be working non-stop while a WHM or AST will have a lighter load.

As far as DPS goes, BRD is likely the easiest, with MNK, NIN, and DRG all being the hardest (due to the combination of melee, positionals, and general upkeep). SMN isn't bad until 50+, but since you're talking about endgame raiding, then SMN is definitely one of the more complex classes. However, if you level SMN, you automatically level SCH, since they use the same base class. If you're looking for flexibility, you can't do better than SMN or SCH.

But again, as noted above, you're going to want at least a handful of classes to pull from. Since you started as PGL, LNC and then ARC into BRD is a natural fit. Alternatively, swap to ACN and CNJ when you can, and then THM and GLD. This will eventually open up SCH (ACN + CNJ) and SMN (ACN + THM), while GLD + CNJ will give you PLD. That lets you pick and choose any role that needs to be filled, plus the support skills from MRD that you use on PLD are all acquired by level 15, so that saves you a bit of work if all you want to do is PLD as your tank.