I don't see a difference in the usage of both. More often do people use 'it was nice to meet you', maybe because it sounds less formal.

nice to meet you at the beginning , when you just met someone for the first time nice meeting you at the end , when you were talking to someone and you wanted to leave him/her.

the 2nd variant is more often in use, and frankly speaking, when i was talking either 2 British or 2 American ppl, they used to tell me "nice 2 meet u" in the first meeting before leaving