We used to fly NW, but switched to UA back in 1999 in order to get into the upper deck Party on the PIP Express. It was a good decision. ^ Since then both
Hunki and I have both been UA 1ks every year. Up until last year we were also both AS MVPGs. We dropped AS last year because if became way too difficult to upgrade the transcons even as an MVPG and, after we closed our PDX office, our need for weekly SEA/PDX trips no longer existed.
On UA we typically take three international trips a year and the rest is all domestic. We love the service. We are almost always (at least 95% of the time) upgraded to first or business. As a matter of fact, I personally have never flown internationally in coach, and have made it a lifetime goal to maintain that record.
Maybe we are just lucky, but we have never really had problems with connections in either SFO or ORD. Even during "the summer from hell" everything went smoothly for us. Back then I was even starting to feel a little guilty about accepting all of the bennies they were handing out by way of apology for our "inconvenience".
We are both closing in on UA Million Miler so it is unlikely that we will switch, at least until we hit that goal. I do occasionally toy with idea of achieving lifetime status on AA before we retire. If we do that it would be primarily the result of credit card spending.
So until we retire, it will be almost all UA metal for us. When we fly places that UA doesn't, i.e. TEL, we fly SEA/FRA/SEA on a UA revenue ticket and then get an award ticket FRA/TEL/FRA. Once we retire we have a huge stock of both *Alliance and One World miles to burn to see the rest of the world.
Our only regular destinations to which AS is really a lot more convenient than UA are LAS, LGB and SAN. Even since we dropped AS status, we have always managed to get first class seats on those flights.