SS - My favorite. I'm not a huge fan of "I'm not strong enough, let me transforming until I am" And one of my favorite moments was when Goku transformed for the first time on Namek.

SS2 - Least favorite. Seemed pointless to me. They look the same. And again. The whole "I'm losing, let me transform a second time" concept is lame to me.

SS3 - Cool. Long hair changed things up. I can actually tell the difference now. But once more, this kills it for me: "I've already transformed twice, I'm still losing, I think I'll just transform again."

SS4 - I actually like the concept a bit more than the previous 2, makes a little more sense to me. I didn't like the black hair at first. But after thinking about how the transformation took place, and the fact that they look a good bit different, it really grew on me. And not to be that guy but, GT didn't actually happen at this point, so this ones pretty meaningless to me as of now.

SSG - I like the way this transformation takes place. The fact that they had to lend Goku the energy and power to transform made it much more appealing to me. Rather than just "let me power up for a fourth time! :D" The look however, sucks. Looks like kaioken.... Except kaioken actually looks BETTER. I feel they really dropped the ball on the design here.

SSGSS - I don't know how it takes place. But my god, really!? ANOTHER TRANSFORMATION? The last movie just introduced SSG and that already wasn't enough? Not to mention, I think the blue hair is not just random, but looks really bad. This is equally as bad as SS2. I would say it's worse, but I'll at least wait to make my opinion on that until I watch the movie.