Both are good to solo with, just depends on your playstyle.
For the moors, again both are good. However, wardens have a lot better survivability than rks, so if your plan is to solo in the moors then warden is your best bet
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.
If you'll be skilled enought to get proper items and push proper skills, there is no big difference between. Otherwise warden, since this class has more survivability.
Ps with "straight hands" you can fight against 2-3 creeps at once on runekeeper, and kill then all