I was looking at the freightliner M2 to pull my 15,000lb 5th wheel. This was based upon comments from many RVers on the medium duty and RV forums. The posts indicated satisfaction with the M2 as a tow vehicle. Comfort and safety were the main indicators.
I found a great deal on a Chevy C4500 that had been upfitted with similar suspension, interior and options as the M2. It tows my trailer like a dream.