I personally don't think it is a matter of what's better but I guess that depends on the 2nd part of the question which is "which is better for ????. If its stock performance, then I think it can be argued both ways, however if it is overall performance then I believe the Hemi has proven itself capable of making far more power with less work. However, if the question is more random such as which is better to own, the answer then becomes more murky as it is a matter of personal taste. Lastly if its a question of value, well thats a pretty straightforward answer in that a Hemi car will almost always bring more money than a wedge car of the same model and vintage.
I don't think there is a true Mopar guy out there that would not not want to have a Hemi, its the epitome of the brand, a thing of legend and thus the quintessential Mopar thing. I have one for the same reason I have a Viper, because it is or was the "king" at one point. Basically for me it came down to this; I am and always have been a Mopar guy, not to ever own "the legend" would have been a void for me.
Now, the last thing I will say on this is that speaking for myself only, if I had a wedge car that I had grown up with, loved and cherished where basically when I look at it I am seeing an old friend, I would find it very difficult to exchange it just to have a Hemi anything.