There is no objective way to decide this, so few controllers have experience of both and none have recent experience.
In my opinion (I stress opinion) Area is harder to learn because it is the least visual of the disciplines (this is not the same as saying it is harder to do, in fact once you are through the learning stage it is probably a bit easier because it is generally more predictable). You cannot gain "the picture" from an Area Radar, you need to build it from the strips or all singing all dancing electronic tools. In a tower "the picture" is right there, assimilated with a glance. I cannot comment on Area v's Approach with much authority but approach radar controller use their radars far more than area controllers do so I suspect, again, they get more of their information visually.
This is a sweeping generalization but I think it largely addresses what LEGAL TENDER says. None of the discilplines are more or less skillful than the others but Area requires skills that are less intuitive and therefore harder to learn, taking longer to aquire.