PHX-LAS can be cheap and requires transiting SFO or LAX as UA does not fly directly. Unfortunately the cheap fares generally have routing rules that only allow transiting one and not both (even though the fare rules allow 2 stops, the routing rules won't). I'm not sure if it's better or worse than SFO-LAX-LAS. The latter could be used to reposition for the former if the times work out.