Hi Brian,
Over at RFF there are about six hundred threads with this question.
I think it would be safe to say there are subtle differences between the lenses. If you read tests and filter the opinions
around the interweb. None are bad, but this one is best. Something about opinions & body parts everybody's got one.
Without trying a couple of them you're not going to know which version you like. I can't tell 'em apart
so would look for the best deal I could find. I doubt that I'd ever pop for the aspheric though.