We have all three types and would not recommend IML or Cessview.
Avantext is the best experience but they seem to be losing contracts (Piper).
We are looking at going with ATP as thats what we use for regulatory stuff and it seems to work well. IML has some real issues when you want to print something. OK from a disc but impossible online unless you want the whole chapter. Cessview it slow to operate and the quality of some of the scans is poor. Hope this helps a bit