With filters, bigger is usually better, but more expensive. Not at all true with pumps. I'm of the opinion that smaller is (usually) better with pumps. The smaller pump uses less electricity, is cheaper, and you can always run it more to get the pool clean. That's assuming it is large enough to handle vacuuming or running whatever cleaner you might want to use. A 3/4HP pump should easily handle the needs of a 10,000 gallon pool.