You need to go look at both of them. The list price may depend on how much the dealer paid for the rig or some damage that you'll see when you look at them. There's not 'standard' like you'd find with car dealers. Usually higher mileage is priced lower, but you say they have about the same mileage.
If the newer one has the same price and mileage and is in good shape, you should consider buying it. It's the one you like the best.
2015 Dynamax REV 24TB class C