Ranked is a good way to get a lot of matches in pretty quickly. Its a good way to fight other new people, Unfortunately you going to play a lot of people doing really stupid random things (so you might learn bad habits). Lobbies are great if you are in a small one, you can keep fighting the same person/people and actual develop knowledge of the character/matchup (they can give you tips too). Jumping into a 8 player lobby with people way higher skilled then you can be a drag though, but you can watch them to see how they play, and you can understand the game better.