OUYA is more of a gaming box where as the Roku is more of a media Box. If your looking for subscription services go with the Roku not sure if they will support the OUYA right at the start or even if all.
Well, the Ouya can run Android applications, so whatever of those services have apps or can run video inside the browser should work fine. It won't be as 'streamlined' of an experience though, especially if you have to use the browser.
So far there is allot of promise for this being a media streamer. The problem will be getting the APK's for the services and loading them. As it stands it doesn't have the Google Play Store. So one of two things have to happen
1. The provideers have to add it into the ouya store and provide it that way.
2. Do a search for the APK on line and sideload it.
Sideloading on the Ouya is a piece of cake, so if the apk is easy to find it can be great. But I suspect some of them won't be easy to find. Fortunately the streaming app I use for allot of stuff is easily avaliable.