Dave, I don't have much experience with ponds but I chose a siphon and it's working out nicely for me. You don't need a long pipe for one thing. The diameter of the pipe can be smaller because it operates under pressure. Water enters your pond at the surface level and the siphon pulls water from deep so you're draining off less desirable water. I would think that in a situation like yours where you have constant flow a siphon would be great because you would constantly be draining deep (less oxygenated) water.
Please keep in mind I'm a rookie, so give the more experienced pondmeisters more consideration.
