I like ORD because:
-Like another poster said, it is roomier, "fresher", a better place overall to be at
-B17 RCC

I hate ORD because:
-Wx can easily be a nightmare.

I like IAD because:
-More miles flying to IAD from my home airport due to 500-mile minimum, if I have a connection (for instance, BDL-IAD-SFO earns more miles than BDL-ORD-SFO)
-Pot Belly and Five Guys!

I hate IAD because:
-A terminal is a dump. 2-3 flights boarding at the same time plus incompetent and non-english speaking agents make it worse.
-Connecting from C1 to D29 isn't necessarily a fun thing to do.