All classes/jobs level at about the same pace. You have multiple ways to level and dungeons generally are the highest exp givers. Though Challange log and fates and other stuff works now as well. And really. You can have all jobs on a single character. Just start and switch if you feel like you need a different experience.

Tanks and healers have fast queue times while DPS will spend a lot of their dead queue time running around chasing fates and stuff so up to you there.