Palm, I use ARM media for mine - dual chamber andd fill them about 3/4 to 4/5ths with media (aprox 2 and 3/4 canisters of ARM).
If I am not mistaken, Moralin recommends what media to use with their reactors, I could be wrong, though.
I like ARM so far, but haven't used anything else - it has lasted a year and then crapped out - just changed it recently to new media, but on the downslide of the effectiveness of the media, I lost almost 3 monti caps (rare ones) - not sure if that was a user defined problem or a media problem. Either way, I am happy with it.
House