In my experience, the added wheelbase of the Suburban is a plus, but the biggest improvement came from going from a 1500 Suburban to a 2500 Suburban. I've had all 3 and won't go back to a shorter wheelbase or a 1/2 ton again.
That's been my dilemma in recent years... My 2005 Suburban 2500 8.1L is a towing beast, but I'm ready for something newer. However, GM stopped making 2500 SUV's, and I've been at a loss as to what I would like to buy next.
After a lot of research, the GMC Yukon XL Denali and the Cadillac Escalade ESV have a lot of the heavy duty parts that came on the 2500 Suburbans - bigger motors, heavier brakes, HD transmissions, heavier axles, etc..., and enough towing capacity for all of my trailers except my 5th wheel.
I've just ordered a 2015 Yukon XL Denali with a 6.2L 8-speed. 420hp and 460 lb-ft of torque, and the latest magazine articles reported 21 MPG in 4x4 version. I'll be listing my 2500 Suburban as soon as my GMC comes in.