What matters more in terms of HVAC systems?

[Tim Coppola]

The brand (Carrier, Rheem, Lennox, Trane, etc) or the company that installs it?

I'm starting to have companies give me estimates for replacing my two rental units HVAC systems and after a little research have come across the notion that the installation has a lot to do with the long term quality of the AC and furnace. 

I would understand not having a handyman doing the installation but can there be an actual difference between professional companies doing the work?