The thing to watch out for with biomedia is that it is not easily clogged and that it still has good surface area and is porous.
I have heard the Eheim substrate pro (looks like cocoa puff's) is the best at that, but have not used it yet, but I have a new Eheim Ecco coming in the mail that has it so I will soon know.
That being said, I have used the Eufilav (crushed lava rock) and I really like it but others say it clogs easily. I have not found that to be the case, but I did not fill it to the rim, leaving ways for the water to get around.
I also really like Seachem's BioMax, and it is not nearly as expensive as the Eheim stuff which goes for about $20 per liter where the Seachem is about $11 for a 2 liter package. The eufilav is also about $5.50 per liter so you can see that I like the Cheaper stuff and as I have no problems that I am aware of, I will probably keep using it unless the GOOD stuff comes with a new filter
