First of all, I'm just going to assume that Mitzy and Skipper are both rat terrier/chi mixes.  I'll never know for sure but I think they are.

Mayfly, the purebred rattie, is the most prey-driven one of the bunch.  She's also the most energetic (i.e. hyper) one and the one who is most eager to please, also the one with the shortest attention span.  She's also the WIGGLIEST dog I've ever known!

Mitzy and Skipper, the ratchis, have longer attention spans and are calmer in general (only relatively speaking as all 3 are balls of energy).  They are less interested in squirrels, etc. but that may also be because they don't see as well.  Mitzy is the SMARTEST dog I have ever met, she actually plans things and manipulates the others, she's cunning....but not in a bad way.  She and Skipper like to learn and to please us but are not as totally into it as Mayfly.

All 3 talk (mutter, grumble, growl talk), fight with their butts and have the same kind of bark.  They are all rather dominant dogs and it's a toss up between Mitzy and Skipper for alpha (after us). 

Just some random observations about the few differences between the doggies!