Hello,
From my experience, WJA seems to have way better service as a whole between the two airlines. When I flew with ACA, the people working on board were pretty brutal with the services provided. Now I was flying the A319, from YYZ to YWG, which was uncomfortable to say the least. I find the 737 is much better for comfort, the tv's right in front make it much easier to watch movies, etc.
On the piloting side, the two flights that I have gone with ACA, came out fairly disappointing with the pilots basically saying "screw off" after the flight. With all of the flights aboard WJA, every single pilot brought me up front and talked with me for a while, and answered all of my questions.
Lots of ACA pilots I know are great guys, some of them just seem they've been flying too long or something.

Saying that, WJA seems to have a more friendly atmosphere.
How was your flight with them? If only one airline was flown, how was that?