One thing to keep in mind is where you go domestically. If you travel to a variety of places that are not UA hubs, you'll be spending a lot of time in ORD or IAH or flying down the back at US. Whether that justifies what I consider a much better frequent flyer program than US -- despite the current integration challenges -- is something only you can decide. For me, MileagePlus works better than Dividend Miles, but my colleagues in PHL tend to stick with US.

I never used my international upgrades the year I was a CP, but I can't imagine that UA's GPUs would be any *harder* to use than them.