What airline should I fly?

Whichever airline gets you there.  I would suggest a direct flight, if there is one offered from your airport, which would mean either Air Canada or Lufthansa.  But you can fly any airline you want if you're willing to do a stop-over somewhere.

The one that has the schedule that meets your needs at the most reasonable cost.

Everyone has their own personal preferences for departure/arrival times, layovers, and cost. We cannot tell you how to decide.

Tick, tick, tick, tick, tick, tick, tick, tick, tick.

Whatever airline offers the tickets to and from your required destinations, on a suitable time and within your budget

The most expensive airline, first class.

British airways if possible. VIP service even in coach. 

Since so many are cancelling flights, you're gonna have to call around and see what's still flying. Good luck.