Pick one
Your OW RTW in coach should generate enough mileage to get you a free domestic ticket, or more. Depending upon your carrier choice in your RTW ticket, pick a frequent flyer program that will generate the most mileage and request elite status prior to your flying. If you don't have any status, and it seems likely from your post, you may want to pick AA and do an AA elite challenge, depending upon how many AA miles you can generate in the beginning of your trip, so that you can take advantage of the elite status, for mileage bonuses.
As far as the DL trip, that will not be usable on any OW carrier's program, so you may want to try Delte, NW or CO for that trip, the miles may amount to some benefit in the future.