Flow and drip?
Anyhow, rockwool is very very tricky if you're just starting out.. you need to be very dilligent in checking your ph levels etc and have accurate testing tools...
I prefer hydroton.. And if you go the rockwool route, don't go cheap, get the good stuff. Funny you should even mention this, I just finished reading an article on the difficulties of rockwool and the article really drove it home to stay away from it if you're a nube grower..
Best of luck with whatever you choose..