Just read the following review:
http://anymoon.com/blog/?p=7161
Tons of pics, comparing the Hasbro, SDCC & Takara versions
Things are looking more and more like I might go Takara for this one, I'm a sucker for added paint apps, also two guns
Downsides are, Takara is the only one that doesn't have black ramps (kind of like them), and the chrome face seems excessive? Maybe will be better in person
Judging by tfwiki, the only difference between SDCC & the Hong Kong one, is the stickers (metallic VS glossy) and the bonus minifigs (red/purple Autobot/Decepticons, VS gold/silver)