- Motto: "Vi Veri Veniversum Vivus Vici"
- Weapon: Vibro-Force Gun
I've never been to either, but the conventions you mention vary hugely in size and scope.
I'd say the Chicago Comic-Con has a much more varied field of pop-culture covered, from movies and TV to comics and toys. Likewise, the amount of people visiting (any) Comic-Con is HUGE, and you are going to have to start enjoying standing in lines for hours. Focus on Transformers will be (relatively) limited.
TFCon is WAY smaller in scale, with about 2500 visitors in total. This means it's much more personal. And of course the focus is entirely on Transformers.
Personally... darn, hard choice. They are so different that I'd actually like to visit both. Although if I would visit any Comic-Con, I'd probably prefer the San Diego Comic-Con to the Chicago Comic-Con, just 'cause it's the biggest (although I do love the city of Chicago).
OK, given the choice, and given what I know about the lines at the ComicCons... I'd choose TFCON!
I'm so meta, even this acronym...