Although really, early first-season Kirk is the exact same character as Pike -- a serious, driven, brooding, lonely starship commander. He only evolved into a different character as Shatner's performance influenced the role and (probably) as the writers came under network pressure to make Kirk a more conventional '60s action hero.
I beg to differ. I think they were similar, but not exactly the same. Kirk was more serious in the beginning, but he also had a sense of humor and at least cracked a smile from time to time.
I do prefer Captain Kirk from Season One over the others, but on the whole I'm glad Shatner had the role instead of Hunter. While Hunter might have been entertaining in a different way, I don't feel like he'd have lightened up enough based on how I've seen him characterize other roles. Shatner has a more approachable appearance about him as well. He's just easier to like.