You can make all the different putties with the same epoxy if you mix the fillers in yourself. This means hardly any waste vs, buying individual putties.
If you run out of below the waterline fairing putty and you need just a little bit more, that half tub of structural putty isn't doing you any good.
Phenolic microballoons are for fairing below the waterline
glass bubbles for above waterline
wood flour,
milled glass,
chopped glass - all structural
silica - used to thicken all the other fillers so they dont sag, can be used as a glue if mixed with epoxy alone
Get a few fillers and a kit of epoxy and your set. I use pre-mixed putties is on very large projects where I know I will use it all. Really, I only use pre-mixed fairing putties as they go on smoother than what you can mix yourself (packaged under vacuum)
My site
gulfstreamcomposites.com has all the fillers and epoxy. free shipping on orders over $200