I would add that in case of IRROPs, and assuming you are leaving out of LHR, AC would provide more rebooking options. BA does not have a OW partner in Canada and being rerouted via the US would add a lot of immigration steps, most especially if travelling with a checked bag. AC has daily flights to YYC and multiple daily flights to YYZ & YUL all of which have frequent and regular service to YVR.

As for service, as with most airlines it can be crew dependant, though AC's service is likely a little more casual (for lack of a better word) which I appreciate.