After much debate I settled on the 12 volt vs the 110 volt version. Simply because I can't always be sure of what source of elections will be available.
The first car I lifted was a friend's Infinity, which officially is to heavy and long for it. The jack did fine, I don't plan on making a habit of going beyond specifications, this car was just easy to do a test. FWIW those of us with early Miatas need to get the 3500lb version. The 5000lb version is too long for the Miata wheelbase. Also Costco and Home Depot sell the 5k version. The 3.5, 5,and 7k versions are available at www.quickjack.com and other re-sellers.