Ron - MicroTrains split off from Kadee in the 1970's to focus on Nscale while Kadee went towards HO. The old Kadee Nscale and new MT (microtrains) are the same thing.
I run mixed trains (Atlas and MT) and have yet to have a serious problem with the Atlas coupler. The early Atlas couplers had problems with the pins falling out, but this seems to be fixed. Each coupler type prefers to match up with it's own (MT, Atlas, Kato) and sometimes need a little assistance to join together, although only MT's have given me problems when it comes to uncoupling.
Atlas has recently begun offering truck replacements that are less $$ than the MT sets, but Atlas doesn't have nearly the selection that MT offers. Kato has a new magnetic coupler, but has yet to offer it seperate from their engines.