Which rosin is best?
The ideal answer to this question might be a counter-question: which eyeglasses are best?
It depends on the individual player and the particular instrument.
Robert Cauer Violins once conducted a yearlong study, giving a box of 20 bows for one week each to different players. The bows were of the same type and weight but had different rosins applied, and each was coded only alphabetically. The cost of the rosins used ranged from a few dollars to $25 per cake, but the result showed no universal preference for a particular type of rosin. Each of the rosins, regardless of price, received roughly the same acceptance.
Of course, this experiment was not perfect because no two bows can be exactly identical in their playing quality. However, the results do indicate that even though rosins are quite different from one another, the perfect choice for one player may not be right at all for another.