Apparently today is the last day for the BA offer. I assume the OP has made a decision by now.

I think it depends on your circumstances to a great degree. Do you already have miles with either BA or CO? Do you have UA miles that you will be combining with the CO miles? Do you prefer *A or OW?

I got the CO card with the 50k bonus miles back in early March because I already had over 50k UA miles and knew I would be putting them together. I didn't have a CO OnePass account before then.

And I just got the BA card approved a couple of days ago about 2 weeks after applying. I had them move some of my existing credit line from my UA Visa card. If you have multiple Chase accounts they seem to be amenable to moving credit lines around so their exposure isn't increased. The rep I talked to even suggested it before I did.

But as others have suggested, CO will go away for good in a couple of months. Since BA has already done this promo twice with a good response I think it is likely to return at a later date.