Orkut has many features, but it's invite-only and still in beta, so it's slow and buggy at the moment. It has a more detailed profile, ability to join communities and most of the features features friendster has. I haven't used it extensively yet but I believe it'll be better than friendster after it's fully finished.
Friendster is popular, open to everyone and very easy to use. But it's usage is rather basic and limited, and as MassZero mentioned before, there are alot of shallow people on friendster that will message/add you just because you have a pretty face. There are many people using fake photos (usually female photos) that have 500 friends (95% of which they don't even have a clue who they are) and tons of testimonials in ascii writings like Cool, Pretty, Cute and so on
It's also somewhat buggy, with users reporting missing testimonials, message sending/receiving problems and pictures not showing correctly.
Anyway, there are several other similar services, so it's up to personal taste.