I think one of the most valuable status perks is free E+/C+ at booking. While you can’t directly compare the elite levels anymore, you need Plat on DL vs only Gold on UA.

As noted *A will be much better for redemptions broadly (but will probably put you in LH’s dreadful J or send you out of the way via Warsaw or Istanbul. But with DL if you accept the $0.01/mile valuation (think it may be closer to 1.3¢) you can redeem domestically or wherever and more or less get treated like a paid fare (eg, eligible for upgrades, earn toward status).

Internationally, UA is behind on the catering but the Polaris product is very good and more consistent than DL’s hodgepodge. Just need to avoid the UA 764 fleet for now (and I guess 757 although DL has the same seats, just fewer of those birds).