A few comments about CO, US, EWR, and DCA:
1. CO service from EWR-DCA is usually late. That is the norm, particularly on Friday afternoons. This really has more to do with the terrible state of things at EWR (my least favorite airport) than CO.
2. US has drastically improved from a few years ago so I'm not surprised at the excellent service you received. (I'm a Preferred level member and they continue to surprise me.)
3. DCA baggage handling is usually fairly quick, especially compared to SFO which has got to be the slowest airport around (maybe its just UA, but I typically wait 20-25 minutes for bags at SFO).