At one time it was not permitted to install an A/H in the attic on NEW installs in NEW homes without enclosing the A/H in its own room. That is no longer the case. The only requirements now is it can be no further than 6' from the access, must have a clear walkway to the service panels, and must be in a space that is a minimum of 36" tall from the top of trusses to the bottom of the roof deck.
If you are on the water I would choose the Trane due to the aluminum coil. If not on the water I don't have a preferance either way, they are both quaility units.
As far as Trane being available to anybody, that is not the case at all. Home Depot does not sell Trane equipment, they simply have a deal to display the equipment and sell you a contractor to do the install while they provide the financing. You can not go to the Depot and walk out with a system.
As stated before buy the contractor, not the equipment they are pushing.