Most of the ones I want to remove just pop free when I hold the legs with one hand and bend the base back and forth. Sometimes the screwdriver/knife/mini-prybar was needed, but not often.
If it's a mech you are trying to remove, I find it helpful to pull the bottom of the dial, the part with the sticker with the numbers and colors, right off, and then bend and flex the upper part of the base with one hand while holding the legs of the mini with the other.
That being said, having just bought 14 boosters from my flgs, the glue is old enough on many of the mini's that they just pop clean off the base with minimal effort.