Im not sure about your specific cities, but I had a rental AYQ to ASP - all companies offered only a set number of kms (like 100 as I recall), and also had drop fees.
If you booked it through Voyages Travel (which is an 'Indigineous Peoples Owned' entity) they give unlimited KMs, and- depending on which agency- no drop fee. For the city pairs I did, one could rent avis, thrifty and hertz... it was a no-brainer- using Voyages was a slight PITA (they arent as easy as an online hertz booking) but when they get their comission it seems like they have leveraged a better deal from all the majors.
Again, having said this I dont know if they do this for the major cities you are looking at or if my observation is only for the NT or other unique areas. Thought it might help someone....