I’d have to say, Gouken’s Super alt, Seth and Dictator’s Ultra alts are my favorites. (I don’t actually own any yet).
I don’t actually use Seth, but if I had that costume, I would seriously use him all the time. It’s the one with the freaky tubes, he looks like some crazy corruption of the tin man from the Wizard of Oz.
As for costumes I wish were included, I just wish Cody had something other than that thuggish wife beater costume and his orange prison jumpsuit. Something out of character for him would be cool.