On the A320, I like the window seats in Row 3. The NRSA's, who tend to be noisy (!), are usually seated in Row 1, and the TSA guy is in Row 2. There's spectacular scenery west of Denver, so I recommend you take the seats on the "north" side of the plane -- you can look out the window w/o getting the sun in your eyes. So, 3C/3D westbound, 3A/3B eastbound.

I've only been on the 757 first class once, but recommend a seat in the middle rows -- row 1 is too close to the forward galley, bulkhead, and movie screen, while Row 5 gets the noise from the lavatory/galley behind you.

Have a great trip!