I've been trying every network under the sun as an alternate or possible replacement for another ad network. Not much luck with any of them so far, except for this one.
I can't make a recommendation based on whether they are reliable about paying on time or not, as I haven't been on board with this one for very long, but as far as the payouts go, it's showing some potential.
Banner rates seem to hover at several cents less than what CPX tends to yield on those, but just a little bit less is still in the "reasonable" range.
Popunder rates have been surprisingly high. Avg. $3.63 so far, as opposed to the $1.40 that paypopup pays, and the approx. $0.90 to $1.20 or so that CPX pays.
So if you're looking for an alternate ad network, you may want to consider giving this one a try
Underdog Media