If you never had one or the other just comment on the one you know about....I wouldn't have a roof air unit----they look funny hanging on a low tree limb. Yes basement units as a rule have 2 compressors (mine does) My basement unit is ducted through the ceiling (won't freeze my ankles) has been serviced regular by my house a/c man without a problem and I can't hear it running. I guess mine is a heat pump because the heat is down there also but comes out of the floor ducts. I don't use the storage bays so that don't matter either......decisions!