I'd really like to know which types of rosin get recommended by violin teachers. Unfortunately, most violin outfits come with the light amber-coloured block that passes for rosin, although I have heard that the darker it is, the better (presumably something to do with the friction? - You can tell I'm not mechanically-minded!)
I use Kaplan Art rosin, and recommend this to my students as well. An adult student used it in her lesson today for the first time, and was seriously impressed by the difference in clarity. (She had previously been using Hidersine amber rosin.) I think there have been previous threads on this topic, but it might be helpful to have a further discussion, especially as there are, no doubt, new brands out there that haven't been covered before.
Also, are there some rosins that seem to be better suited to particular strings? I'm currently using Obligato, and my adult student is on Helicores.