For miniatures, I prefer to use a putty, like Green Stuff, Milliput or even ProCreate. Your miniatures are the focalpoint of all your games, and also need the sturdiness, as they get handled a lot. besides; you really don't need a lot per base, so wouldn't be all too expensive.
You
could use wall filler, clay etc, but they dry rather brittle and the wear and tear of battle might mean your basing work might chip off the base itself (or washer/coin whatever you tend to use)...
My € 0,02
