We used Office Ally for 2 years via their Practice Mate.
For the price it was fine.
We have recently purchased Medisoft and are using Gateway.
They strive for (guarantee?) a 95% 1st pass rate.
More cost, but less hassle.
Whenever you change Clearinghouses there will be some lag.
Be sure that you can continue to submit to your old clearing house until you are up and running. When we went from a private billing company to doing our own it was months before we got up and running. That was a very tough time.
At least now, we aren't paying a % to the third part biller. We do pay a monthly fee to Gateway, but they seem to be all over it and very supportive.