I would choose AC any day for the following reasons:

- 180° lie flat pods
- decent food
- generally very good service
- access to Maple Leaf lounges (which are much better than any US lounges)
- more miles if you connect in Canada vs. flying non-stop

I would probably even choose AC C over UA F, but I´m sure some other FTers will disagree on this one.

If you asked me for a ranking:

1. AC C
2. CO new C (pods)
3. UA new C
4. US C
5. CO/UA old C