If I didn't need Origin for Mass Effect and Battlefield 3 then I probably wouldn't have it, as others have said, there's just no real reason to use Origin over Steam.
That said, I will say this for Origin: It's a lot more stable than Steam is. Steam runs like crap, it's a great program, I love it and I love Valve, but seriously, it's unstable as fuck. You inexplicably get disconnected quite often, you get errors sometimes just going from the store page to the community page, I got an error message 5 times in a row just trying to add a video to my profile once, hell, lately Steam has had problems signing me in automatically. I've lost track of the number of times I've had an error when it's tried to sign me in automatically when I turn on my PC and I have to end up signing in manually.
Origin on the other hand, is perfectly stable, I've never had any errors while using it, never been disconnected from it for no reason, and for some reason I actually get faster download speeds on it than I do on Steam. Origin is pretty much devoid of anything Steam has, apart from a store and a profile page (that you can't even do anything with) making it shit compared to Steam, but at least it's shit that runs well.