Easiest? Robots/FF with Medicine pool for Aid Other. Really good build for learning the AT, and they are all ranged, so park them with a GoTo command and let them do their thing. Bubble and spot healing as needed. Safer, but slower kill speed than demons.
Most fun?
Demons/Dark. Lots more to do, speedier kill speed, and super effective debuffs, no knockback to fix, smoother ride to 32 than bots, since the pets are less back loaded than Bots, and damage ability is spread out more evenly. Need better situational awareness than FF since your survivability is tied to your debuffs.