I'm actually midway through the first season of Arrow right now. I'd say I would have to choose Daredevil over it based on the ten episodes I've watched of Arrow. It's a decent show, but you can tell the CW made it. Everyone in this show looks like they stepped out of an Abercrombie ad. It's not a bad show or anything, but I think Daredevil was a lot more interesting, dark, and coherent.
Arrow, thus far, seems quite a bit less serialized than Daredevil. Yeah, they've got the plot with the list carried over from episode to episode, but by and large each episode deals with a different villain and is mostly self-contained from the other episodes. Daredevil, on the other hand, largely tells one story over the course of its first season. I greatly prefer serialized television over "monster of the week" style storytelling (which is prominent on network television).
One thing I really liked about Daredevil was how they focused on the physical and mental toll getting beat up every night took on Daredevil. He gets his ass kicked a lot on that show, even in the fights he wins. There are a couple of episodes that are focused on him recovering from said ass kickings.
Daredevil also gives equal time (at least in later episodes) to the Kingpin, and paints him as an interesting, deep villain with realistic motives and willing to do terrible things to accomplish them, all the while telling himself that he's the good guy trying to redeem his city. I haven't seen that at all from Arrow yet. All the villains are pretty much just evil for the sake of being evil, and the show doesn't spend enough time on them to give them any depth.
And yes, Daredevil is very dark. Much darker than Arrow. The body count in the first season alone was pretty staggering, especially since none of Netflix's brief promos really gave us much idea what to expect from the show. If you haven't read the Bendis run on Daredevil, or Frank Miller's "Man Without Fear" trade (you should definitely read both, by the way), that's about what you can expect from the show. The best non-Daredevil comparison I can come up with is some of the darker Batman stuff, like the Arkham video games. The main difference is that Matt Murdock is a lot more likable as a character than Bruce Wayne has ever been.
So yeah...watch Daredevil. It's a pretty good show.
