Dealt is better for tight players. Contributed is better for fishes.
On the other hand, dealt creates an incentive for rakeback pros who play a nitty break-evenish kind of poker but profit from the rakeback. That makes the sites using dealt rb like pokerstars
and fulltilt nitfests compared to sites that use contributed rb. It's particularly a problem at pokerstars at stakes where you can aim for supernova+ (mostly 200nl). So the games are often juicier at contributed rb sites.