I am looking to book two tickets to USA late July come back mid August. I have accumulated 300k+ miles and I am looking for advice on best options

Preference is direct flight flying in to Philadelphia back from Boston

My questions

a) which is best experience American / US Airways or BA - I have done CW a number of times and find it a bit claustraphobic and Envoy does look more spacious

b) Does booking a premium economy seat and then using miles to upgrade represent better value

c) Ex EU options are not viable as other half doesn't want hassle of changes

thanks all in advance for any information