It's been a while since I've played those games, but last I remember RoM was my favorite of the three. It's very much a WoW clone, to put it bluntly. A quest-based leveling system being the main point.
Cabal and Conquer weren't bad, just lacked any real content besides the straight-up grind(Though Conquer had some basic PvP, never got far in Cabal.).