Welcome to WebmasterWorld Guest from 184.108.40.206
You're right about the *Seem*. It can be hard to work out exactly what to expect. Both of these companies take the full amount up front, but pay you after the guest has stayed (they have been sitting on the money in the meantime). Some companies just take a non-refundable deposit as their cut. One thing to check is what their cancellation rate is - they keep 100% of the deposit on cancellation (nothing for you).
I've used TN and have to say the setup and support is a breeze.
I would suggest either WCTravel or TravelNow as having the best programs available at the moment. There are a lot of factors that need to be considered, in my experience the companies trying to attract affiliates with a much higher commission cut often have shoddy data and integration options.