Originally Posted by Knitette

If it's available here, I usually go with what the pattern recommends. I prefer a type of bag that has some 'form' to it and is not so 'floppy'. For fusible fleece, I much prefer Pellon 987F - so much so, I imported a bolt form the US. It's thinner and stiffer than the one at my LQS.
For interfacing, I use Vilene heavyweight. I have used the Medium too, but found the lightweight virtually useless.
There's an Interfacing/Fusible chart here and gives the US names too.