Thanks, William-James88 for answering a bunch of these questions for me, but yeah, let me address a couple more details in here.
Unicron - wouldn't count for this list, as he was introduced first in TF: The Movie, waaaay back in 1986.
Windblade - wouldn't count for this list as she was a toy first, and then used in both cartoons and comics.
Minimus Ambus - Yup, WJ88 is right on that score. He was a comics-first creation before we got that kicking toy.
Nova Prime and Scrounge - Both of these two WOULD be eligible for this list now that they have toys. The problem, however, is that when I wrote this list, it was at a time when neither were released. Nova may have been mentioned, but Scrounge and the Computron boxed set were barely a glimmer in Hasbro's eyes.
Zeedust is right: these are toys whose characters would have originated in the comics.
That being the case: Sentinal Prime wouldn't totally work - but I'll leave the ultimate decision to you all. Although the recent Titans Wars figure is based on the Megatron: Origins Sentinel Prime, he is not the first to have that name. The first that we saw was mentioned in the comics, but then we got the Animated Sentinel Prime, and then the late Leonard Nimoy's Sentinel Prime from TF: 3. So what do you think? Would this count for the list?
WJ88 is also right in that this isn't about the quality of the figures - if anything, this is more about the characters: who they are in the comics, what they bring to the stories, and how they have affected the fandom. As a novelist, I'm all bout consequence, and so I err towards how these characters, and stories (like in my top 10 G1 episodes list) impact either the fandom or the actual universes of the stories.
And yes, Noideaforaname, you're right. This IS a pretty specific list, but it's one that was born from the ashes of my previous list:
http://www.seibertron.com/transformers/ ... yet/34221/.
Thanks for the questions and discussion! I'm enjoying reading your responses to it!