What about Bumblebee as alot of people know who he is so you could have i.e. G1 Minibot - Classics - Movie - Animated quite diverse and small in size to carry.
Maybe G1 Mirage and Classics Mirage too

And for Bots and Cons at least G1 Prime as everybody know who he is. Grimlock, Starscream and Soundwave again popular for the masses.

First Season Optimus Primal and Cheetor would be good as well i think. and then maybe a pred transmetal like Rampage or TM2 Megs

If you are thinking of bringing a combiner team Stunticons would be a winner

As for showing off the engineering and puzzle factor Movie Leader Optimus i would think be a good one as its not too hard and not too simple to transform (still might wanna practice)

the possibilities are endless....and some rare japanese one would be cool too HEADMASTERS!!!!

with whatever you decide Good Luck and Congrats!! hope to see you on TV!!!