Hmm this is such a hard question, not sure there is really a real answer.... I am mainly a shakehand player myself, but I will play some penhold every once in a while for fun, and I still can beat almost the same people with it as I do with shakehand. And I probably honestly have the best rpb of anyone I have ever met.... which isn't saying that much.... because I haven't really met very many.... My blocking and mid range rpb sucks, but I have become pretty consistent and good with counter hitting and flipping with the rpb. And then just naturally, the forehand for the penhold seems better in my opinion. I don't quite understand why a lot of people have talked about wrist problems being caused by penhold.... You have such room and freedom to move with your wrist for penhold, and its so natural compared with the shakehand, that I would think it would lead to far less injury.
Ultimately I would say that penhold, in the larger picture is probably better, now that the rpb allows a penhold player to basically have just about as good of a backhand as a shakehand player, the penhold's utter mastery of the short game is just too hard to beat at a high level. You are simply too good, if you are able to control the short game with first a penhold superior serve, then the short game allows you to attack more often then not. And not those attacks are so spinny and high quality that you are able to win the point more often than not.
That having been said, I think it takes a lot of time, training to get to the level of skill required to take advantage of the serve and shortgame that penholders have. For those players who play for fun, and just to get good, without making it a profession, the shakehand has a much easier learning curve, and in the same amount of time playing, you probably will be a lot better of a player as a shakehand than a pendholder.