American Express is offering 15,000 bonus miles with first purchase and first year free for taking their Delta card.
The page has a live link to an offer for the Delta Business American Express, first year free with 12,500 bonus miles — though the page says the offer expired February 28th. You could try to apply for it and my experience is you’ll likely get those miles. Or you could play it safe and go for the first year free offer with 10,000 bonus miles.
Note that you could also wait for a direct mail piece, which gets sent out pretty regularly to Skymiles members (though I don’t know which ones) offering the business card with 15,000 bonus miles at signup plus 5,000 miles for each of two additional fee-free cardholders.