Since you already have quite a few miles on CO and CO has no Starnet blocking that UA does, I think CO could be the best option for your primary carrier.

Do you expect to spend $30,000 a year on flights? If you can pass this threshold with flying 250K miles, then focus on CO to get the Presidential Platinum Elite status.

Otherwise, it is a good idea, as you suggested, that you could try to reach 100K on two carriers, say CO and AA. You get 8 eVIPs a year as EXP and other benefits. And all miles collected from not only flying, but also credit cares, car rental, hotel stays, etc., are counted toward the status of lifetime Gold (1MM) and lifetime Platinum (2MM) on AA.

With 250K flying a year, you can reach the top tier in two legacy airlines of two major global alliances and enjoy the perks.

In term of delays, you might want to take another perspective. If you have some flexibility of time, delay and irregular operations could bring bump opportunities, in other word, free $$ for another travel. As top-tier, you should be well-accommodated when delay or overnight bumping comes.