From what I understand, Win Shares can give a player a boost, specifically if his team has excellent defense, which will greatly up his Defensive Win Shares. So while a good defense needs all five dudes working in harmony, I'm of the opinion that Mike Conley Jr. and George Hill (#11 and 12 this year) might be benefiting a little more from their teammates.
Meanwhile PER (and it's Value Added spinoff I like to use on ESPN) barely even includes defense and often rewards usage/chucking.
I'm sure there's something wrong with Simple Rating.
Regardless, they are all nice ways to reinforce what you are seeing happening on the court, as I'm sure all you guys are aware of.
I just prefer PER because our players come out better in it.