God of War 3 always felt a bit anticlimactic to me. I liked it fine, but did not care too much about it. I think it was because I never bought that Gaia not helping Kratos because she needed to hang on herself, was this big problem that led to Kratos turning also against the Titans. And it was very dark and the levels felt somewhat samey.
Previously I would have said GoW2 is the best. It really felt like a step up and the action was cool. But again, in hindsight this time, I was not very much interested in the conflict between Kratos and the Gods as presented in part 2. He destroyed a city, became pretty much Ares 2.0 and needed to go. ... Alright I guess.
Part 1 presents something more interesting to me. He is tormented. And he slaves away at the gods commands in hope to get rid of the trauma and that he can finaly sleep without the nightmares. That does not happen and he tries to kill himself. But the gods would not even allow that. If we saw Kratos tormented, plagued by visions in part 2 and 3, I would have liked them much better.
So they are all very good games. But part 1 is the best for me. Also because it feels so memorable. The temple with the rings on Kronos back. The desert. Athens. The sea. Hades. The final fight. (-to echo what op said) It was such an adventure. It still feels epic even if it is small by todays standards. In part 2 there was a temple. And another temple. And the titan shouldering the earth for a short level. And yeah, it felt somewhat less memorable.