Everybody has a different opinion, and I guess I may as well give mine...
1) Blue foam is the best but you may have to try a few times to find the right amount of material to use
2) Pyramid tea bags are good but too much of a hassle when you can just use blue foam
3) White fish
tank stuff (fluval) I have not used
4) Anything is better than the polyfill
Having said anything is better than polyfill, there are many who swear by using it.
But they cut it down and only use part of it.
Also, if you are motivated enough, you might want to try the Buff Puffs.
There are some people who think those are the best, but I've never bothered trying them.
I switched to dripping instead, but you might want to check out the ZFM mod first, which uses no filler at all.