It depends on the condition of he material your blasting. I have a bag of black beauty that I will never use. Its just to expensive and although its good I don't think I've ever blasted anything requiring that rough cut.
I have a 5gal bucket of plastic media but hardly ever blast anything that I use it on. It will ONLY take off PAINT.
I've used the FINE that GMC Gold mentioned and it does good on most anything. I use it "almost" exclusively in my cabinet... I also used it outside on my nasty rusty 52panel chassis.
To each his own and you'll find what works for you. As mentioned a good 3M respirator will work for most stuff you blast.
Do a search on sand blasting and you'll get hours of reading and opinions. I base mine on my experience. You'll do the same.
EDIT: I also have a 50 box of glass beads I use on certain delicate stuff. Soooo, I guess if your gonna be blasting much you'll need a little of everything
