I would say that the Heads in http://i271.photobucket.com/albums/jj125/Gizmojunk/heads.jpg and http://i271.photobucket.com/albums/jj125/Gizmojunk/GHOULS.jpg. They have more style & character (even if they have less animation frames). That said, I love the art in FO3, I absolutely love the feral ghouls, and "Glowing ones" [And DeathClaws too]... But I don't understand why they chose not to use a more detached dialog interface, but with vastly enhanced NPC heads (in somewhat the same ratio as FO1 had with the combat sprites and their dialog heads).
Well, I'm personally not of the opinion that the talking heads from the originals really hold up all that well to modern standards (they have that sort of "claymation" effect that was common of FMV at the time, I was just never a fan of that.) Though, looking back I do agree there was a bit more "character" to them than you often see in Fallout 3. (All faces in F3 are created with FaceGen - while it's a lot of fun to mess around with and you can get a nice consistency with it; you just don't have that individuality you can get with making them from the ground up.)
That said, I'm not really sure how much added value you'd get with implementing higher-res talking heads for the main characters. For starters, I don't think most players beyond fans of the originals would have understood why they were doing that; I don't think most people would really notice that much of a difference. The whole "zoom in to the NPC you're talking to" is a pretty standard and natural interface for a game like this - it could have been done differently, but I'd have to see it in action to be able to really say if it was such a better choice.
Not to mention that the "talking head" characters would have had one head for when you see them out in the world, and another one that they change into when you talk to them. It worked really well in the originals, but no one had any other head for you to look at. With F3 when you're exploring in first/third-person, it might be a bit jarring to talk to most NPCs in a certain way, and then to see something different when you talk to the main NPCs. I mean, for better or worse, every NPC you talk to in F3 already is a "talking head" of sorts.
I think possibly a good compromise might simply be more of a focus on the animations of the main NPCs when you're talking to them. One thing I do sort of miss from the originals is how you could affect their mood through dialogue choices and see that visibly represented on the NPC. Just adding that might be a good step in the right direction. Most NPCs seem to use pretty stock animations that are shared over all models (idle animations, etc.) If the main NPCs had more individual animations, maybe if they were rigged in a more complex manner than other models, you might get a lot of the same effect from the original games.
You could probably even get away with having the faces of the more important NPCs built by hand rather than with FaceGen to give a bit more character to them - it likely wouldn't result in any more polys for the game to render, and if done correctly wouldn't look out of place in comparison to the other models - they'd just stand out a bit more.