I can confirm Nessaj's recommendation.
h264 in some form is the way to go.
It might be impossible to record and compress h264 live, so my best bet is that you record in something with a mild compression, then convert it to h264 later for web distribution or upload to youtube.
Recording format should have mild compression, because no compression would tax your drives immensely, and too high would tax your cpu too much.
My 1080p h264 quality settings in quicktime is set to halfway between medium and high. It's a nice compromise between quality and compression.
Don't forget to also compress the sound in some way, as it too can take up a lot of space.
* MPEG streamclip is a great software for batch-converting large numbers of files.. and it's free.
* Test your workflow with small files before you do the big thing..
very important that.
good luck!