In my experience ewr-las is worse for upgrades. I don't think it is very plat heavy because I have been number one on the list on Q/U fares when I have missed. The issue is more of paid first selling out. I think las-ewr is better because there is a fair no show factor. Also avoid the 752s if you care a lot about the front because the people paying for it seem to know the 156º seat exists.