Simliar situation for me last year, left SkyWest for SWA and decided to update the 'current employer' section of my apps in the middle of SWA training.. United and Delta both rang within a week, after about 6 months of crickets back at Skywheezy being fresh in the left seat.
I'm local to the Bay Area so I had OAK/SFO to choose from depending on the airline, similiar to having your pick of airline in DEN.. For me it came down to what would give me the most time at home and the least gray hair over the next 30 yrs.. My last flight with SWA was my IOE sign-off trip, currently home-based on the WB side with United.. I've been averaging about 1 trip every 5-6 weeks. Granted that is apples to oranges in comparison to the NB side.
Being able to choose your flavor of flying with United, plus the benefits of DEN expansion and the Training Center I think make it an easy decision if you plan on staying in the area long term. I had a fantastic experience going through training with SWA, and all my classmate buddies over there coming off probation right now are all happy campers.. I would happily have stayed if I didnt get the call from UAL. You have the benefit of choice between home-base airlines, hard to go wrong.