More than a poll, you need to make a decision based on your own needs. Price, features, even hotness
(I mean how comfortable you feel with the service, support and such)
You'd also inquire on custom solutions, or even packs like Mambo for CMS.
As for clickman's... dunno. I wouldn't advice to, but as I said before, you'd try different choices. We had a pretty unsatisfactory experience with them, to the point we ended using CCBill's own CC features and it worked way better than Clickman. And getting a mod done could take a lot of time. We ended with a full custom solution, more expensive than NATS and MPA3, but way more affordable in the long run and when adding more programs. However, I wouldn't recommend the custom way for processing, the optoions you mention are good enough
