Here are just a few. (Disclaimer: I use and love LastPass, but am familiar with 1Password).

Sync- it's possible with Keychain Access + Dropbox, but not seamless

Easy password generation- no switching to Keychain Access, copying, etc.

iOS access- up until iCloud sync, passwords were not easily transferred to devices

Support for Windows browsers

Form filling- Keychain will do addresses, but not credit cards