Actually, to some degree, I have to agree with you Brent. At first, I thought Grievous was quite, well, lame. But he's really grown on me lately, and seeing that statue on display at C3
really opened my eyes. At this point, I've got to have it, so since it's only a preorder at this point, I just want to be sure my name is on the list. I can always change my mind later.
As for Vader, I don't have the Koto, CinemaCast, Gentle Giant, or Medicom versions (some still preorders, obviously). I think the sheer size is what blew me away about the Sideshow Vader, even though I like the GG pose just a bit more.
Overall, for absolute

power, I'd have to say the General Grievous is the better of the two. But Vader
always has power over me.

And so, I've got both pre-ordered.
If these companies keep it up, I'm going to change my focus from Hasbro to these statues full time. Time will tell.