I agree mostly with Gallus' list on page 2.
If you want to relax, picking a class that is hard to mess up and fairly forgiving if you do mess up.
NIN and BRD are pretty far up there with a super easy/no proper rotation at all. If one of the extra moves becomes available, hit it. Done. If you drop your DoTs and have to spend 2 instead of 1 GCD to refresh them on BRD, yeah, it's annoying, but the dmg loss is minimal. If you drop your self-buff on NIN, and have just used the Mudras for something else, getting a bit slower for like 15 seconds is a bit annoying, but your DMG output won't go down by heaps and bounds.

On the other hand, you have classes like DRG and BLM that operate on extremely tight timers, and if they get messed up even a bit, they drop your DMG by a lot.

Of course, like others have said, each class is hard if you are aiming for the optimum, but if you are satisfied with being "decent" and don't want to put in too much work, those low-risk jobs are the best choice.