I've only tried the Verizon FiOS and YouTube apps and I'm not impressed with either.
The FiOS app is pretty pointless. You don't have access to all your channels, you get nothing else extra for watching on the 360, and you can't record from the 360. The only reason I would ever use it is if I'm recording two things on my DVR and there's nothing on my DVR I really want to watch on the moment, which doesn't happen often. I would have liked access to things like HBO and Cinemax or be able to record shows but as it stands, I'll likely never use the app.
For the YouTube app, I have I believe 11 other devices that can use YouTube in my home and the 360 app is one of the worst ones. The interface is nice but that's about as far as my compliments go. My big complaint about the app is that after you watch a video it doesn't show you related videos to what you just watched or more videos by that user.
I was browsing through the popular video and saw a video I wanted to watch. I watched it, liked it, but then I had to go back to popular videos. If I was on a good YouTube app, I would have been able to watch related videos or more videos by that user but on the 360 app I have to go into the search option and use the awful controller search (can't even use voice commands!). If I'm really yearning to watch YouTube on my TV, I'll just stick with AppleTV and Air Play.
