Awesome price -- go for the 10 gal. You might not find the 5 gal for much cheaper anyways.
If you batch sparge, there are basically no advantages to the 5 gal (unless you physically can't find room for the 10 gal cooler to store it). Otherwise, the 10 gal has some major advantages (let's you brew higher gravity brews or bigger batches, plus you can store a major amount of gear inside when not in use, you can stick carboys inside them for fermenting (e.g. add ice for lagering), or they make a great keg cooler, etc.)