OS X/ iOS Password Managers
1Password started as OS X-only, so it's more popular among long-time Mac/iOS users. Their Mac/iOS support should (theoretically) be better because it's their original platform.

That said, I use LastPass on OS X and iOS (and, occasionally, Windows and WebOS) and I'm quite happy with it. I haven't heard of any one cloud password management being significantly particularly better than its competitors nowadays.