The goldfish has been bred in many varieties all of them are tame none agressive
I however would have to pick the ones that are closer to their wild brethren not for looks but for the ease of keeping them
"fancy" goldfish are prone to intestinal diseases that cause dropsy, bloat, and death
If you are willing to deal with a fish that has been proven to get diseases go for it
the one i would recommend would have to be the comet goldfish (i like the long fins)
the reason why fancy goldfish are shaped so strangly is because when they were first bred they were not kept in glass tanks where the owners could see their sides, but in large bowls and ponds. So the breeders bred the goldfish to have an "appealing" shape when veiwed from above.