Amalur has a better story but thats just because DD has no story. Combat i think is better in Amalur but not as challenging or rewarding in the sense of beating giant monsters. Bith games have lots of hours you canput into them but made reason id get kingdoms if i was you is because a better version of DD is coming out in a few months i believe.
both are great....tough choice, but I put more hours into Amular so I'll say that, very rewarding gameplay in fights
Dragon's Dogma is fun but it hits a point late mid game where it's just no longer challenging at all, in the beginning you're so careful moving around because a ton of stuff can kill you and then later on practically nothing can
KoA is more more fun at the beginning, but the world doesn't really pull you in and combat gets easy REALLY quickly. I've only played that game on Hard mode, and even then I was wasting everything in my path by level 20 or so...Dragon's Dogma can still challenge you through NG at least, so it stays somewhat fresh (despite all the walking/backtracking you do in your first game).
I also felt that Dragon Dogma's world was a lot more interesting...a lot of people bag the story but I did feel that the NPC quests were interesting and, compared to KoA, felt a lot less like endless fetch quests and more like actually helping people. That was good.
I'm also a big fan of dark fantasy so obviously KoA doesn't win there. Dragon's Dogma has a good bit of grit to it, while KoA is...comically dark, at best.
I dont have either but based off the demos I'd say DD just because it's also getting the expansion, the giant monster battles seemed more challenging and visually impressive, and you can has Berserk armor and Berserk rocks, plus Amalur has that weird Worlds of Warcraft meets Dragon Age look to it which I don't like...