If you're someone who actually enjoys using LastPass, I don't really know what to say.
The UX (and design) of 1Password is way better.
But another important reason is that LastPass is a central service where you have to (at least somewhat) trust them to not screw up since all your (encrypted) passwords are on their servers. With 1Password there is no such mandatory central service.
I'd say the only reason to use LastPass is if you're cheap, or if password-sharing is a daily exercise for you.
Another reason to use LastPass is if you use multiple computers. (I use 5+ computers at work in tech support and 2+ at home.) Using 1Password would require that I install the desktop application on all of these computers, whereas with LastPass all you need is the Chrome extension.
Have you tried the 1Password Android app? It's uglier than anything Lastpass has ever put out. I've paid for all Agilebit's apps switched to Lastpass because 1Password's multiplatform support is shit unless you're stuck in the Apple ecosystem.
So, I actually use 1Password on iOS, Android, OS X, and Windows on a regular basis. OS X and iOS are clearly the most refined versions of the app. The Windows version is fine, and as far as I can tell does everything that the OS X app does, but it looks like a very workmanlike Windows app and nothing like the OS X app (which might be a feature for some Windows guys, who knows). Anyway, it's fine.
The Android app is read-only. It gives you read-only access to your 1Password database in Dropbox, but that's it. It works, but they really need to give it some love and bring it up to par with the iOS version.
I was briefly a user of LastPass until that service lost every credential set I had added to it. I tried a KeePass store in DropBox for a while but the poor cross platform support and mobile support got me to try 1Password. For what little it's worth I've been very happy with 1Password so far; superior UX, cross platform support, and control of my own backups.
I found it to be possible but difficult to get KeePass running on every machine I want a password store on. When I last used it running the KeePass itself under Mono was an annoying install process, slow to launch, and far from a native UX. Sorting through unofficial contributed ports to find working smart phone apps (and trusting yet another party to manage access to my password store) was also less than ideal.
I'm sure it is possible to get KeePass working smoothly but I'm also happy to have paid for what feels like a better solution to me.
The UX (and design) of 1Password is way better.
But another important reason is that LastPass is a central service where you have to (at least somewhat) trust them to not screw up since all your (encrypted) passwords are on their servers. With 1Password there is no such mandatory central service.
I'd say the only reason to use LastPass is if you're cheap, or if password-sharing is a daily exercise for you.