I imagine the reason you are seeing higher fares is because neither AC nor WS are posting their best fares. Hence the advice not to book to far in advance.
I want to nuance the advice favouring WS over AC. This is good advice, if:
- you live near LGW;
- you don't care if you collect Star Alliance points.
My understanding is both WS and AC fly 787 non stop ? If so, you can't say WS is better then AC ?