I get more credits in less time when I play full games, because it's possible to get more points in the last two levels than it is in the first three. For example, I usually get between 1300-1500 points for playing the first level, but can often get 2000 for level 4 or 5. 1500 points = 300 credits, 2000 points = 400 credits. So I would not make as many credits to keep playing the first level over and over. Not to mention the time wasted going to the lobby and waiting for the next game to start.