What are criteria to compare and evaluate different 12 inch truss Dobsonian telescopes?
The cooldown fan is purely to speed getting the primary mirror to the local ambient temperature. It is not used - and should not be left on during observation, as it'll undoubtedly be a vibration source. 

That shouldn't be a significant factor in your final decision.  I would go with total weight, and perhaps adaptability to an equatorial mount for star-tracking.