Are the contractors planning to install units with the same sizes? I know Phoemix gets very hot, but 9 tons is a lot of cooling. Did either contractor do a heat load calculation?

You need to understand if each contractor is providing equivalent equipment and services. Can you provide a list of model numbers and what each contractor will be doing as part of the installation? This may help in justifying why the Trane quote is much higher than the Rheem.

FYI: Trane makes American Standard. AS is usually cheaper than T in all sizes. You might want to see if you can get a quote on them.

Trane is probably the most expensive brand out there. Rheem makes good stuff but doesn't carry that very large price-tag. Rheem uses scroll compressors and their units have plenty of features. They could be easier to work on as I've known some techs say that Trane's can be a pain to work on. I would consider the rheem if you want to save some money.

Units are comparable. Calcs show I have about 48,000 cubic feet (4,000 sq ft home with vaulted ceilings), so I believe the 4 ton for upstairs and 5 ton for downstairs are accurate. Model numbers are as follows: Rheem - RARL-JEZ (compressor) and RGPE (gas furnace). Trane - XL16i (compressor) and XV80 (gas furnace). Air handlers have separate model #s, but are hard to read on the estimates. Other than described above, the estimates match as far as work to be completed and parts provided. Great idea on getting an estimate on American Standard, as from what I can see, they are rated higher than Trane, although part of the same company. I assume pricing may be better, as you aren't paying for the higher advertising costs associated with Trane. Feedback I have heard is Tranes are more expensive to repair, and a bit of a pain as well. Good idea on the extended warranty option on Rheem. Still undecided, but feel I have a better understanding now. Thanks much for the input!

Either unit will give good service if properly sized and installed. If the installers are of equal comptenece then warranty provisions should be the deciding factor. Is the warranty service totally free for a specified period or will you be charged trip fees? Not getting a clear understanding about things such as trip fees and such can provide some nasty finiancial surprises when warranty service is needed

Look past hardware brand name and focus on specifics of extended warranty. Don't make the mistake of believing the more well-known brand will deliver superior reliability in service.