I always enjoyed being DM in the past, seemed they always answered the Diamond Line quickly when I called, the GUC were awesome flying BKK-PHX because you could book Y and get Delta One Suites on certain routes, I got picked up by the Porsche in SEA a few times just to get ferried to the Skyclub, the extra Choice Benefits were cool as I was able to gift GM to my sister (who was flying frequently with my little cutie goddaughter) and that was awesome during Covid days with upgrades MSP-PHX on international metal and “real” biz class (not suites though), plus the Choice benefits got me a free Sky Club membership (which was cool but this used to be free for members living in Asia - well it was way back mid 00’s) — so yeah a lot of the benefits of DM aren’t as good these days as GUC will only get you from Y to Premium Economy which isn’t bad but isn’t D1. Still I would say the 4 GUC as a choice benefit alone is still worth the extra spend. That’s my opinion. Me, I’m doing everything I can to get to PM as I need that Skyteam Elite Plus for lounge access in ICN where I often have 10+ hour layovers on way to USA from BKK or Phuket. Good luck!!