What is your total combined weight expected to be?
I have driven both chassis, however our M2 had the Mercedes and the Columbia had the Detroit-lablled valve covers (not that it matters, they are really the same except the valve cover logos!).
The M2 is a great chassis! For drivability, it feels nearly like a pickup. Around town, its just much more drivable, with better visibility, more nimble handling, and traditional Allison automatic.
However.... even with the Mercedes engine it could not pull hills at its 80,000 GCWR rating. At that weight, it would be be in 1st gear on a 7% grade, so maybe 12 MPH. The Cummins 330 would be even less powerful, and even in first gear narrower operating RPM would slow hill-climbs even more.
The Columbia however can pull hills. At weights that would bog down the M2 the Columbia/450 can keep up with traffic just fine. It's smooth, and the 12-speed shifts nicely (they do offer an Allison automatic but its a $30,000 upgrade IIRC). It is a big truck, and feels like one in town. It does not have the pickup-like feel of the M2.
So really, it comes down to how much weight you will be moving, and what kind of areas you will be doing most of your driving. I suggest some test drives so you can decide for yourself. Penkse has migrated to all new Freightliners, so you could always rent some trucks for a long-term test drive.
2000 Ford E450 V10 VAN! 450,000+ miles
2014 ORV really big trailer
2015 Ford Focus ST
