Like Waggelton said, its down to play style and goals. Both require you to plan your skills ahead of time; no emergency one-click bubbles. And neither are superior to the free classes, just different.
Wardens use chain-combos like arcade fighting games. Button mashing is ineffective so you're got to memorize the combos and know which you want to use next or you'll be warggie chow. Properly traited and played for the Moors, Wards are most survivable class, to the extent that many creeps would rather avoid you all together and go for the squishies.
RKs work on an attunement mechanic. You have to use smaller hits/heals to work tune yourself deeper into dps/healing; save for a couple exceptions and tricks, you don't have access to superheals while DPSing, or superdps while Healing but your avalible HoTs will keep you up just fine while soloing above level. RKs are a threat in the Moors, and are therefore targeted early by creep raids, so don't roll one if you're after stars.