I did a comparison. I tried to book a relatively simple November flight using ATM (Calgary-Paris-Douala) and ITN. ATM came back with garbage and error messages (which Travelocity will also do). I could simplify the routing to Toronto-Paris-Douala and ATM could handle the routing but came up with an outrageously expensive fare.
ITN provided me with several options that were priced appropriately (lower than ATM by $2000). ITN also showed me seats available in different fare classes so I know which flights are likely upgradeable.