I also like the top two pencil versions the best, as long as they fit his personality. Like Bobi said, he looks "crankier" - it's because of the pointy, arched eyebrows coming down in the middle. Eyebrows are a big part of what gives a character their expression, and the shape of these make him look grumpy. So, as long as he's a grumpy crab, it's good.
If he's not supposed to be grumpy, but you want to keep a cat ears element, maybe spread out and exaggerate the ridges on his back?