given the domestic nature of my trips I think my "miss list" would probably be down to about 2 - 1st class seats and route frequency.
Frequency to SoCal isn't too bad in comparison, and it depends on where you're going. Monday 12/13 schedule:
LAX
F9 6
UA 9
SNA
F9 4
UA 5
SAN
F9 5
UA 5
Frontier has Long Beach but not BUR nor ONT.
United has Burbank and Ontario but not LGB.
The Frontier departure time choices on LAX don't seem to have any critical shortcomings compared to United -- both have a wide range from early AM to late PM both directions, though of course UA has a few more choices during the day. Of course it all depends on your schedule needs...some people couldn't live without a 6:00am flight and other people wouldn't touch a 6:00am flight.
Any opinions on the stretch seating? Is it just seat pitch, or are the seats a bit wider too?
The seats are conventional width, but at least in my opinion the added personal space from the legroom makes width less of an issue.
I'm a legacy Midwest flyer who spend many years in the wide 2x2 seats on the DC9/M80/717, and at 6'3" 220# I'm not tiny. Stretch is definitely not as roomy as the domestic F/J seating on narrowbody planes like I experienced on YX, but I'm fairly happy with it. The perceived width isn't bad, in part because the Airbus and Ejet family is a wider cabin the some competing airframes. And the significant extra leg room adds useful personal space, which makes the whole thing feel more comfortable. What I definitely do miss greatly is the width of the armrest, not only because both people could use it, but because it put the passenger next to you just a little further away.
Stretch is not as good as F by any means, but it's a notably better experience than the regular seating IMHO.