Thank you for chiming in, that is precisely the use case I was hoping to hear about! Even though I'm more UA loyal than AA (or WN), I guess I always have this null hypothesis of AA via DFW for intra-TX traffic, so to the extent I was "looking for" this answer, it was to make sure that the UA via IAH option is "not terrible" or better, and not a situation where anyone with a choice takes AA for TX flying (WN too).

To the above, if the IAD n/s works, that is of course always going to the simplest, but as with a good number of DCA p2p flights, the late evening timing means that if plans dictate getting their earlier, you might as well hop a connection instead of waiting around all day. Slight negative preference against the IAD option merely for that timing aspect, and the logistics of getting there either during the afternoon westbound Beltway rush hour (coming from MoCo), or waiting around several hours at IAD (and actually then probably getting into the peak afternoon IAD departure rush through security and all that)....which to me usually mitigates in favor of the connecting option from the more convenient airport. Even when both options leave from DCA, I typically gravitate toward a connection at some point during the day rather than waiting around until evening to depart, unless my schedule dictates that.

The nice thing is that basically any trip I can foresee making will the leisure enough that we should have full flexibility of playing with all the options.