I much prefer Pellon 987F fusible fleece for bags - so much so that I had a whole bolt shipped from the US as my LQS doesn't stock it and I got fed up always paying shipping every time I needed some! I find it thinner and stiffer than some of the other fleeces, so the bag 'stands up' nicely.
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However, I know that some people don't use fusible at all - they spray or glue baste - and rely on denser quilting to prevent floppiness.