I had good luck with UA C class last year, but was thoroughly unimpressed with it on my trip last weekend. As a 1K, I can only marginally recommend United in its current state. As a 1k and 1p I was upgraded on almost every flight I qualified for.

With AA you can upgrade any fare to business, although I'm not sure of the success rate. Also, with AA you get bonus points for Oneworld partners, whereas with UAL, you only get base points. AA also seems to have more bonuses and may allow double upgrades.

Sometime the grass seems greener, but right now United is an extremely unfriendly company.