So, to pull out the really important point from LSLGuy’s post:
A320s have extra width of 18" in the cabin. This means that the six-across seats are likely wider (it is possible they have a wider aisle, too). But do you, the paying passenger, pay any attention to whether you are going to get an A320 or a B737 on your trip?
Didn’t think so. 
Heck, I will, now that I know about it!
What I look at first is number of stops. I hate stops. I had to fly fron San Francisco to Seattle once on business (training) and the company scheduled flight was four legs at 7 hours with Continental. I paid a small premium for a 2 hour nonstop on Alaska Airlines.
My supervisor caught some flak even though I paid the difference myself. Continental is our preferred provider, and Chevron gets a (secret) kickback.
If another airline had wider seats, I’d likely do the same.
Screw 'em.
Would that be the same Seattle that Boeing did not consider to be worldly enough so they moved to Chicago? At this time, other that some small part assembly and delivery of Renton built airplanes, Boeing has nothing to do with Seattle. Even the airframe tags installed in 737’s reflect this, they use to say The Boeing Company, Seattle Washington. Now they say Boeing Commercial Airplane Company, Renton, Washington. Those of us that work at Boeing for a living want to let the world know exactly where we are, and it’s not Seattle.
Have to agree here. We don’t fly often, and last year took our first plane trip in 10 years. I can’t say we felt any more cramped than we had been in the past, either 10 years before or through about a decade before that.