It is no contest, I would take the 350 every time over the 250, it is far smoother and quiter and even a remapped 250 wouldn't match it for torque. I would suggest you try them both and I think you would make the same choice. By the way it is a V6 motor not straight and regards your earlier post Adblue is on the Bluetec engines not the earlier Blue Efficiency.
Straight 6 i was referring to a standard 350 as opposed to a mapped one.
As long as I can achieve more than 42mpg, I will go with whatever engine does that.
Thanks