What to tow my car with a 05 Tahoe or 07 Suburban? Any advise is welcome.

Do not make a choice dealing with gas mileage. Which one is set up for towing? The larger vehicle will be stronger, better to control on the road, and have that better towing transmission and HP. The larger engine will keep the speed up and gas consumption down in the long haul. No pun intended. The larger tow vehicle will give better road control and stability. If that is the only reason you'll need the vehicle for is to tow, consider renting one when you need it. No insurance, no parking issues, no car payments on a gas hog when you not driving it, and it is always a new one.

Thanks for the info, what I am looking at doing is trading in my truck for one of these SUV's, I want it to carry all our "stuff" and be able to tow the car once in a while.

Size matters. Let your macho out. Consider a turned in lease vehicle, low mileage, depreciation already gone, and if it is set up for towing. You can tell if it has been used a lot by the feel of the shocks, wear on the hitch and other things. It will cost a heck of a lot less then a new one, and what you want, you can have money left over to add. Most leased vehicles will come with a great warranty, and consider getting the 100,000 mile warranty. Enjoy and have fun. New one may offer better gas mileage, but the engine is smaller, transmission beefed up? The difference in cost of a new one vs. extra gas cost for a 1 1/2 to 2 1/2 year old one will be advantage to the used one.

The best advice I can give like John below don't go with the Suburban you're going to get about 7 miles to the gallon but you're going to get a lot of pull