also consider the DL reserve AMEX card. It's the 4th tiebreaker on the upgrade list.
And don't underestimate the value of getting access to the special customer service line for Diamond members. Calling that number saves so much time.
Obviously.. SLC has more than it's fair share of Diamonds, but unless you're flying to a hub city you should expect a lot of upgrades.
For me - since they've changed the upgrade ranking order, I get upgraded nearly always. So often that I've stopped paying for F. And most of my upgrades come at the 5 day window.
For me, the tiebreakers are very favorable.
#1. I'm Diamond.
#2. I pay for EC to ensure I'm higher on the list.
#3. My million mile status is normally the highest on the plane.
It's not clear to me if 360 members are counted above Diamonds on tiebreaker #1 - my guess is that they are. And obviously people using regional or global upgrade certs would be ahead of me. Still though, the current system is great for me (and others who fly DL regularly)
I've been very happy with DL. They aren't perfect but that's not the standard. The standard for me is how do they compare to the others. My take is that they are superior to the others on 90% of flights I'd want to take.
Here's the priority list for tiebreaks. It shows the importance of having the reserve card.
Good luck!