__________________ Kevin & Prim Li Bandit the Siberian Husky & "G" the Min-Pin Cosmo the Custom 2008 27FB Intl CCD
2008 Ford F-250 King Ranch Diesel 4x4 AKA "The King"
WBCCI # 11809
AIR # 6155
2nd love - 2006 28' Safari LS
1st love - 2004 19' CCD Bambi
Long wheelbase (120" or above, IMO) and short rear overhang is the quick answer.
From the 1960's and '70's the full-size cars (not Ford or Chevy or Plymouth, but Oldsmobile, Dodge and Mercury) and larger were the "better" tow vehicles due to longer wheelbase (122", 124") and the luxury cars were even longer (127", 129" and 130"; except some Lincolns).
By comparison, a current Suburban is about 130".
Depending on the year and model the rear overhang might be pretty long, a Suburban was sometimes better (though, recall, the half-ton trucks had brakes and axles no better, usually, than the big cars). By 1977 the favor had swung towards trucks as cars had been downsized a bit too much in wheelbase and in powerplant options.
Independent suspension is another relation to look act. Andy T/Can Am RV has made some comments worth looking into, here, other boards and on Web-available articles.
Were I starting from scratch I believe I'd be looking at a Ford Expedition as the baseline for "best" full-timing TV and make my comparisons from there.