The lilydale school is ( in my opinion ) quite nice and would be the best of the 3 you mentioned. Reasonably new Archer III with GPS and older other units. Close enough to CTA and satellite strips. Interesting terrain nearby. 10% weekday discount I think. quick taxi..
EN just too expensive and looong taxi times eat your $, you'll get plenty CTA experience going into EN and MB from elsewhere. I've sat lined up on 17 for > 5 mins twice - it kills!!
Can't comment on coldstream, is that a satellite field of RVAC? It's a solid 20 mins drive further than lilydale.
My 2c!!