I work in the equipment industry and the company i work for has been both a dealer for Allied and Stanley, we are still a Stanley dealer. They are both very good pacs, the question is service that you will get after sale, both from your dealer that you are going to buy from and also from the manufacture. From our companies experience on a dealer side Stanley is easier to deal with. In fact Stanley will even make a new out of commission product if we ask nice, now thats pretty cool. Now i might be shootin myself in the foot because that company might be the one i work for, but five hours is a long ways away.
If this is going to be a heavily used tool then you will need parts and you will need hoses and if down time means money lost you might want to go with your Allied dealer. If you can wait a day or two for parts then go with the Stanley. Of course if your Allied Dealer doesnt stock parts for the pac then you're SOL anyways.
For me, between the two, it comes down to service. If your Dealer down the road has good people and they are a respected business then go with them.