I believe talking in person is the best way to go, the person (whether it is a potential employer or not), can put a name to a face and really connect with someone. Over the phone is a little less impersonal, but better then over the internet. Over the internet is harder to really get a sense of someone because you never really know if it is them that is talking to you or not.
Although it is the other way around when you talk about convenience. Over the internet is the easiest because you can connect with a large number of people, through many different websites, any where in the world, quickly. Over the phone you can talk to someone any where in the world, but only one at a time. Then there is in person; you have to pick a place to meet or be at a conference or just plain luck to connect with others.
Networking is the best thing a young professional can do, the more you can meet, the more opportunities. Then as you mature in your career, those connections can become someone to lean back on and ask for help when needed. Those connections can become your friends and colleagues, and then you can become a young professionals network. The cycle just keeps going.