Orkut has a clean and minimal interface compared to Hi5.
Hi5 seems to be more on the feature-heavy side with you being allowed to customize the background images, and these days even add a song/video to playback on your profile.
I guess ultimately it depends on the network most of your friends are on.
@greenhorn: The problem with all online social networks getting diluted is that people are more keen on having the largest possible friends list, largest number of testimonials/scraps, etc etc. I remember reading a funny forward saying such folks should probably stand at a traffic signal to meet many people :lol: .