I’ve never used Nito, so I can’t speak to that and since I just bought my Apple TV (yet to receive it), what I say may not be entirely accurate. But I have extensive experience with Plex and have done some research on XBMC so there’s that…
The primary advantage of ATV Black (in my mind) is that it integrates the media experience with the traditional Apple TV experience. This is a far simpler end-user solution (which, if for nothing else, is prefered by your less tech-savvy family members who might use the Apple TV). ATV Black is built solely for the Apple TV and is thus more ideally suited for Apple TV integration. XBMC and Plex are more general applications.
Plex and XBMC provide a completely different user experience, but at the moment might be viewed as more mature software than that provided by ATV Black (which, for example, doesn’t scrape TV metadata yet, although my understanding is that this is planned for future releases). While I’m not sure about XBMC, Plex also let’s you add various extras like the Daily Show, Hulu, Pandora, etc. which might not be available on ATV Black.
My plan is, in the short run, to use XBMC until ATV Black has all the necessary features I require at which point I’ll switch.
I’m not sure how familiar you are with XBMC or Plex, so I’ll delve into that a bit.
Plex was originally forked from XBMC although these days I’m not sure how much of that remains. The user experience, however, is still clearly inspired by XBMC. I run Plex on my Macbook Pro and, in my opinion, it’s the best HTPC software available right now. It’s not without it’s share of annoying bugs, but it provides a lot of flexibility in meta-data scraping not currently available on XBMC or ATV Black.
Before delving further into Plex, I need to highlight that it is what is termed a “thin client.” That means that the actual server software has to be running on a Mac/PC on your network. This offers a number of pros/cons (this is far from an inclusive list).
More processing power means greater capability of the server software. The Plex Media Server is capable of transcoding and delivering practically all your media to your Apple TV, IPad, IPhone, etc. (including both MKV and AVI files).
More uniform experience across multiple clients. Start a movie on your computer in your home office. Pick it up on the Apple TV in the bedroom. Watch some of it on your iPad right before falling asleep. Finish it on the way to work on your iPhone/Android (with port forwarding, you can watch your media over 3G). All of it will have the same metadata.
- Requires server software to run. If it’s not available on your network, you can’t access your media with it. Moreover, if someone wants to use your computer to play games while you are watching a movie, that could become a problem.
In fact, this con is why I bought the Apple TV in the first place (I was considering buying a Mini, but this is far cheaper). I was tired of hooking up my MBP to my TV to watch movies and then being unable to do other work on my computer at the same time. And while I could still use it as just a server for the Apple TV client, I’d rather not tie up any processing power. For this reason, I’ll initially use XBMC on my Apple TV (which is a full client) until ATV Black is ready for prime time (I’ll continue to use Plex for other tasks, such as watching movies on my iPhone).
Sorry if this is more info than you cared to get, but I hope it helps.