If we are talking about an $ 8,000.00 job and there is that much of a price difference, I would wonder why and what is one guy providing that the other is not.
If this is a $ 25,000.00 job, that is not that much of a spread at all.
Which variety or style of shingle from each contractor?
Special manufacturing warranty for an extended period of time or standard contractors workmanship warranty?
For how long?
Subcontractors, misclassified 1099 supposed employees, or actual employees dedicated to the companies success and continually trained?
What testing credentials for the installers?
Is either choice of shingle being offered with the AR, Algae Resistant granules?
Have you looked at each contractors current job in progress and spoken with current customers to get feedback from their dealings with them?
Has either one of them addressed the Vetilation?
How and with which named products?
Exhaust Ventilation only or also addressing the Intake aspect of the Balanced Ventilated Attic?
That last one is Critical!!!
Without a properly Balanced attic ventilation system and/or enough Total NFVA calculated for the attic, the manufacturers warranty is Null and Void from Day Number 1.
Which proposal is the most descriptive in writing, naming the brands of products to be used?
Was anything spoken about and promised that is not clearly written in the proposal and not added in as a written addendum?
If it is not in writing, it does not count.
Gut feeling also means a lot.