Originally Posted by
PMMMDL
It is all about perspectives.
Apparently you think the trade-off of possibly not sitting in J class on a long haul flight occasionally worth the difference between a Delta M fare and a lower priced upgradeable ticket on UA (as you said, 95%).
I am personally not willing to take that risk (on AA or UA or any other airline including Delta), and I have found availability of advance upgrade seating (at least on AA where I have SWUs) generally unavailable. I can generally find the Z availability on Delta on one routing or another.
So a question, and I would really like to know the answer. Assuming I am buying M fares typically about 2 weeks out and have not much flexibility on dates, would I be 100% certain of always being able to get an upgrade using miles or SWUs on DL.