I fit both of these requirements now so personally I'd pick B6 because I want to stack more points for the TATL rollout that's coming. DL points are near valueless for my travel at the moment. I'd consider the hard products mostly even with B6 having an edge in faster free wifi as GW mentioned.
If I was traveling for business with hard time requirements I'd probably choose DL.
As to the second posted question, prices are variable but at T-14 I'd book it. Very unlikely to decrease as airlines expect last minute business travellers to suck up the higher priced tickets.