considering this kenworth t700

Hello. i wonder if you good folks could take a moment to share your opinion due to your experience with kenworth trucks and cummins engines. I would like to ask if you could give me your your views especially engine-wise on one of two trucks am currently considering. Both are 2012 model yr trucks.

1st.Owner operator owned kenworth t700 with 350k miles 18 speed 3.25 rear and a tri pac apu.
It has the isx15 cm2250 motor 500hp that has had extensive work done to it of late. Updated ecm software, dpf/doc filter cleaned 6 month ago, fuel pump ceramic plunger campaign performed in jan 2015. Also done in January; new Def doser, valve adjustment including removal of cylinder head and replacing of the valve guides on the exhaust side, also the block and liners were cleaned and the liner protrusion inspected and passed ie ok'ed. Also replaced were the rocker shafts and jake rockers and the overhead adjusted to spec and finally a new egr valve installed on the truck.
I test drove it and it pulls and shifts proper. price $ 85k

2nd tuck Freight Cascadia- Prime fleet owned DD15 455hp 10speed and 3.36 rear with 360k miles.
It also seems to be in good condition (not much in terms of repair records provided) with a rig-master apu and has new tires and brakes all round. Dyno test and blow by results indicate a healthy engine.
It has a sqeeling serpentine belt that we suspect is the tensioner but the dealer is hesitant about replacing claiming its the belt that's bad even though they look to be in in good shape.
price $ 82k.

whats your thought on the cummins engine and kenworth... reliability-wise considering you have experience with them and overall whats an ideal buy between the two for an individual getting into owner operator-ship.
Thanks for your time and opinions