From what I have seen and this is in most cases, not all cases. But in most cases, single click gets more clicks, but a lower RPC. A 2 click page allows people to drill down a little more, but give you less clicks, but usually a higher RPC. Which makes more money that's up to the domain, I have seen it both ways. It also depends on how much traffic you are getting. If you are getting 1000 hits a day on a 1 click domain, you could possibly kill the keyword over a few weeks/months, I know I have a few times. But if you are getting 10-50 hits a day and it's a very targetted domain already, you will probably do better with a 1 click.
Donny