Check the 2004 LT80 first, I believe its a good year for this machine. Getting new and better tires or even with new wheels is easier and cheap like combo deals from these sites:

ATV Wheel and Tire Kits - 4WheelOnline.com
http://www.jcwhitney.com/tire-and-wh...1711j1s17.jcwx

 

I would say the 70 "IF" it had suspension. Once the kids get good at riding the rigid fram will beat them to death. The 70 is a very reliable motor, but ten years older and much more complex and expensive if you have to rebuild. Plus, the 70 will be less powerful and you will need to teach them to shift. For those reasons, I would say the Suzuki, bump the start button and smile.