I personally never minded IAD, but for me the decisions was all untility. 98% of my travel was international so IAD was a no brainer. DCA would have been much more convient because of location and security (though I have heard that DCA can also have some nightmarish security lines). I would say that if 50% or more of your travel is international, then maximize UA MP and use IAD. If it is less, than you may want to look at DCA.