Delta and American Express have upped the sign up bonuses from now through April 28th, 2021. Some have more than doubled.
Delta Gold Personal Amex: 70K miles
Delta Gold Business Amex: 70K miles + $50 credit
Delta Platinum Personal Amex: 90K miles
Delta Platinum Business Amex: 90K miles + $100 credit
Delta Reserve Personal Amex: 80K miles + 20K MQMs
Delta Reserve Business Amex: 80K miles + 20K MQMs + $200 credit
https://card.americanexpress.com/d/cm/delta/