These guys are both right, but another thing you may want to consider is the same generator could also be used at home if for some reason the electric power was to be out, especially in the winter.
The most common sizes are from the 5500 - 7500 watt range. See how many 110 outlets they have, some also offer a 220 outlet.
So, the best solution is to find a good brand and warranty and get as much power for your money that you can afford