I think LAS is one of the easier upgrades, although IAH seems to be better than EWR, maybe because they usually put larger aircraft on that route. They used to have 753s on the IAH-LAS runs, not sure if they still do. One time I did a standby LAS-IAH and actually got on the earlier flight in F. Try to do that out of LAX or SFO. But as others have mentioned, it all has to do with the day of week and if any big convention is in town at the time you want to fly.