Go for Spine.
I can't say I have experience with Dragonbones, but at first glance the features of Spine were just amazing. Plus its platform-independent IDE is also very nice and its many runtimes make it future-proof.
Things such as Inverse Kinematics really makes the game shine, and allowed for ragdolls to look fantastic, without having to use heavy, real physics bodies for each part.
That said, Spine runtime IS HEAVY. We reduced the initial amount of bones from 14 to 9 and saw a significant decrease in CPU usage. The more bones you have the more transforms are ran at every frame, and while QuadBatch helps, the CPU gets hammered anyway. I think this was necessary for us because our game has up to 8 Spine characters on screen, running at 60fps. If you have a single player game without the networking overhead of ours, you'll be fine.
I'd like to ask Daniel if the performance of the Starling extension for Spine could be improved 🙂 The best change we have done to that was adding Spine culling to stop transforms and rendering when not on screen.
Anyway best software purchase we've done last year alongwith the IntelliJ IDE 🙂
