I personally really admire Ikariya's Starscream and Jazz:
Getting to see all the detail and layers he put into the parts....
But LionBoogy's is up there probably at second too! :) Otherwise, Pilot's work is so clean, and I would say I really admire that, though I haven't managed to see any of her work irl yet. :[
Everybody else I've seen irl is amazing too. I love seeing all the different techniques people use, the materials, and the interpretations of the characters....It is what helped inspire me to be such a cheapie and still attempt costuming. :o)
And whatever minor spotter experience I have too...It was a blessing to be able to help Laserbot somewhat as Jazz, and I was SO GLAD she brought him out again for 2011. I thought I missed my chance to see him irl, and then blam, I got to help spot for her! :) :) :)