Get a big motor and low gears in the rear axle, like a minimum of 3:73, and at least a 6.0l engine, or if you're looking for a mid 90's model, go for a 454 in a Chevrolet, or 460 in a Ford truck.
I just bought a 97 Suburban, and it has the factory tow package, the right gears and a 5.7l V8. It is just barely enough, but definitely not overkill for my 25ft tradewind. This truck would be relatively anemic with a 31ft. trailer. For comparison, I also own a Dodge Ram maxiwagon B350, which tows as well, and pulls a lot harder than the Suburban. It's just much stiffer when empty and not fun to drive unless it's loaded to it's max capacity.
I guess the best and safest choice for a beginning tow expert, is a long wheelbase and a big enough motor, and small enough gears in the rear end. I would tow a 31 foot trailer with the Dodge, but not with the Suburban 1500
You will find many interesting opinions, and even some posts with real experiences in the tow vehicle forum.