Okay, here goes. I say, for the most part the penholders have a real advantage.
I am going to put Ryu Seung Min at the top of this list. It is all he has but his forehand is amazing. Not really behind him but next to him, I am going to put Ma Lin and Xu Xin. Xu Xin's forehand is amazing, it is probably the fastest at this point and he gets such amazing angles; and Ma Lin's forehand has been a killer for over a decade.
I think there is a different edge that the shakehanders have but the pace and spin of their shots are not quite the same and the shakehanders do not get quite the same angles. Here is my shakehand list, Wang Liqin (I sort of have to acknowledge history), Ma Long. I personally think these two are the only shakehanders whose forehands look about as good as the great penhold forehands. They are just a hair less in my opinion but the versatility of the shakehand style and the added advantage of the backhand so they have not lost anything on the penholders but...those penhold forehands are pretty awesome.
I think if he gets some maturity and under control people at some point might be talking about Fang Bo's forehand. Not yet though.