First I would throw out the quote from the salesperson that trashed another manufacturer. Ho obviously as a person lacks respect, integrity and other personal traits.
The sales person that I admire most is ones that promote and highlight their own products, not degrade others. The fact that he attempts to put doubt in your mind about aluminum coils leads me to believe he is defensive and knows or at least thinks they are better.
A HVAC company should be selling their own benefits company first, application second and name brand products last.

Trane/American Standard has been using aluminum on their outdoor units for years, and introduced the indoor aluminum coils about 3 years ago. To my knowledge, they are the only ones with 10-year free factory parts on their coils.

From TraneÂs site:

"With a strong heritage in aluminum outdoor coils, Trane has applied our innovative thinking to develop the industry's only all-aluminum indoor coil. Rust resistant and almost corrosion-free, our all-aluminum coils set a new industry standard by preventing leaks that often occur from corrosives like salt or common household cleaning products."

Copper prices are three times that of aluminum. That may be a factor. Then again, maybe not. Below is a thread on the subject with HVAC pros doing most of the talking.

Here is a link that might be useful: Aluminum Versus Copper Thread