SMN.

SMN might even be the easiest DPS at level 60; you learn how to execute your desired opener, and you just do it. Any changes in the fights are usually pluses to the rotation, like multi-DoTing or getting some stronger Painflare/Deathflare action and with some practice, it's really easy to know how to adjust. Hopefully you have a preference for a lot of buttons though, if you're on a controller be prepared to swap between 2-3 pages of commands constantly.

BLM presses less but has the potential to get screwed over much harder. It's not exactly rocket science but you can't just learn the rotation and go do well, you're adapting many things to any fight at hand.