Why use twitch.tv?
Twitch has no mandatory commercials after the one when you log on (IDC if you just say 'adblock adblock', some people dont use adblock and therefore HATE IT and miss important stuff.)
Speaking of ads, if you channel gets popular enough on Twitch, you can make money from ad revenue. This program is public, meaning ANYONE who reaches a certain level of popularity can AUTOMATICALLY make money. Ustream only allows a handful of channels to make money.
Twitch.tv has an amazing "dashboard" from which I can see chat, get a small preview of my stream, AND change the title of the broadcast, AND play commercials if I wanted to from the same screen. It helps me a great deal while streaming.
Twitch has a much better chat. Allows me to make/remove custom censors, etc.
This may not be important to you, but Twitch puts SERIOUS investment into competitive gaming. They sponsor tournaments and players (especially in SC2), and double the money made from many charity events run through their streams.
Twitch responds to requests! The site is run by an awesome team that isn't afraid to actualize good ideas.
Finally, Twitch works harder to help my channel grow. Their site is videogame players only, and they do their best to help channels be successful through related channels and search results.
These reasons were compelling enough for me to dump the old channel I had (50 followers and 4k views in 4 months) and move to my new one (now has 283 followers and 16k+ views in a month and a half.) Loving it.
BTW Wario is super good in P:M, and I was having more success with him than with Pit yesterday. Thanks for tuning in everyone.