Looking at Lennox and Trane, I just cannot make sense of the differences between the various AC units that each manufacturer offers. How can I make an informed decision if I cannot even understand the differences between the various models.

For Lennox/Trane among all their AC unit, which ones are the one you would recommend (pro and cons) and which lennox is comparable to which Trane. Looking and searching through the site, it looks like Lennox HS26/Trane XL14i and HSX15/XL19i are the preferred ones and often compared.