I'll echo ssullivan's sentiment and say that UA has improved - no real big in-flight issues with them this year, and I'd say better than NW service.

Did have one CSR at ORD bark at me earlier this year about refusing to put me on the upgrade list when I was on a full Y ticket (and entitled to a free upgrade) - got 10k miles from UA for that incident (works for me considering it was a 45 minute flight to MSP and I was in an exit row).