I would rather have the 13 speed and Detroit Diesel engine, rather than the 5 or 6 speed Allison auto. Mainly because you have more gears to keep the engine in optimum rpm. I assume the 13 speed is an autoshift type? The Mercedes engine is not bad, it is actually quite similar to the Detroit, but it does have reputation as being a weak engine brake capacity. Which chassis is the Dynamax, I assume also Freightliner? I think you are good with either mfr, both been around and make good quality. Like many responses for used RVs, a lot depends on how it was maintained, both are out of warranty at this point.
2005 Kenworth Showhauler truck conversion.
. 44 ft, Cummins ISX15 450 hp, 10 speed, twin screw
I used to have a handle on life, but it broke