With a question like this, you're probably going to get a lot of biased options. Not because people want you to use an inferior product, but because obviously one think that what he uses it the best. For example, as a current KeePass user, I'd suggest it.
Lastpass overall is comfy, you do everything within your browser, it sync without much problems and you can use it on the go with the official applications and addons. One downside is that everything is closed source. The other one is that I find their addon is trying to do too much, and it's not polished enough (at least, their Firefox one). I've had tons of annoyances with it.
Keepass instead is awesome because it's opensource and you own your data. But you can feel that not everything is nicely integrated. I use a Firefox addon (PassIFox) for filling username/password, and it works pretty nicely, but you have to set it up (and it's kinda a pain to get it working on Linux). I use an application on Android (Keepass2Android) which has a different UX, and doesn't have the fancy input method that the lastpass app has (instead you just copy/paste, and there is a keyboard for autofilling but I find it mostly annoying). The integrated sync support only ftp/webdav, and not everyone has a server providing those around (and I never got webdav to work anyway). Sure, you can sync the file with dropbox or other "cloud" solutions, but this implies even more software in your chain.
I never got to try OnePass sadly, as there's no Linux version.
Anyway, I'd say: Try both, and see which one you prefer. Keepass is libre, and lastpass has a free tier, so you don't have to put any money in it. Just use them for a bunch of sites for a bunch of days, and then decide.