DCA is a YX 170 base. You only get benefits for what you support. Therefore, you're eligible for AA benefits (which are pretty bad, honestly). You will not get Delta. You can get UAL benefits but pay the non-supporting rate, which is $200 for you and an additional $200 for each person enrolled, plus segment fees. UAL is not worth it unless you're based somewhere that supports the operation and get it cheaper. Just jumpseat on them for free.