Feels to me like the muzzles are too long and/or heavy. Narrowing them and shortening them would help define what sort of species a character is.

Hmm maybe deatzh, but at the same time I think this makes them more distinctive in another way :). Some more playing around might be in order but this is a good exercise done well. Only problem I can really point out is the ears seem a little far back on the left most pic. The slightely open mouth on the frontal view in the middle is interesting :). Yeah I'd say keep playing around with these, they're neat :)

SUDDEN REALISM

I do enjoy the softer look in these busts. I hope you continue this trend.

I think the top left has a bit of twist comparing the ears to the rest of the facial features.

On the right, DEM EYEBALLS. For a pupil and iris that large, the eyeball should be tremendous.

The weird pointy bit of hair on the rightmost one stands out as a little weird. I love the expressions of the other two, though -- you're building character. :0