I've used both. I would use 1password if you really only use one computer (or you use more than one Mac and sync via Dropbox). Lastpass if you use more than one computer, or want to be able to access your passwords from the web. Interface-wise, 1password wins, hands-down. Lastpass is little more than a browser plugin.
The biggest difference, for me at least, was that 1password stores data locally, and Lastpass stores it "in the cloud."