I don't envy you the juggling act of dating so many at once - but if you have several good prospects, I do think it's appropriate not to just jump at the first one, but take some time to get to know more about them.
And once you choose someone, I think the politest (polite-est? Most polite?) way to let the others down is to tell them you really enjoyed meeting them, but that you've decided to move forward with dating someone else that you met around the same time. Maybe someone4 else here could word that a little better.
As for me - my new guy told me this weekend "I want to call your ex up and THANK him!!!" lol.
