Way to ruin the fun.... I think they all have there different little cue's though.

R&T's looks like a regular SS with a slightly larger hood scoop, a 3 layer grille, z/28 emblem, and bumble bee's front bumper (with the fog lights flipped upside down.)

M/T looks like bumble bee's front bumper (completely painted though) with the fog lamps dug deeper, with a 2002 camaro SS hood scoop. And rims similar to the new Z06

Bumble Bee looks.... better in the first Transformers

 

From what I was hearing guys..this is (was) going to be the Z28. Just like the first TF movie this was supposed to introduce the new Z28.

But this was back when the pictures first surfaced and the movie guys were saying Z28 BB...for what its worth..

 

Out of those three pictures I think Bumblebee looks the worst. It does look pretty wicked in some of the straight on shots and I'm sure it will look good in the movie. It's been fairly common speculation that Bumblebee hinted at the Z/28 and I'm sure that Motor Trend and Road and Track both used Bumblebee as inspiration for their renderings.

 

The little opening on the SS is a mail slot... but the one on the Z28 renderings is definitely not a "mail slot".