I really don't know, actually. However, I feel (though I can't really back it up) that Shockwave is older than Flash, it started around 1990 I think. So if you want to make online games, you'd probably want to go for Flash AS3, instead of Shockwave.
If your looking to make quality online games I would suggest going with Flash. I havent used Shockwave so im incapable of speaking on the difficulty of the program but, Flash keeps faster loading and game speeds, overall the software is much more capable as well.
