I don't see many running from AS to UA but I agree if you are going in and out UIO UA is convenient if nothing else. I have been down to Quito 3 times now over the last 2 years out of SFO through IAH and it wasn't a bad connection. I think maybe it was a little over an hour. While this may add a stop you could also try routing through SFO, the PDX to SFO flights are like buses these days and this may save you the 5AM departure. The Centurion lounge suggestion is great given the quality of UC clubs at IAH. As noted it is not a "Polaris" flight but who knows that may change.