Using Delta is more expensive, but it has advantages.
You don't need to worry about bad weather during your drive. You don't have to worry about long term parking and you don't have to fly through Toronto.
We used Delta this past March and the flights were excellent. The partner out of Boston was Song. We all had in-flight tv and games at our seats to help pass the time.
The only reason AC has lowered their rates is because of Delta. Before Delta started servicing Fredericton, their prices were incredible.
The other advantage is that you don't have to take a road trip and possible extra hotel stays to get to and from the airport.