When you find the one that you like the most, that's the one you will use all the time.
Except when your milk changes
I agree with Sailor. The point of checking for flocculation is to help guide you to achieve a final moisture level in the curd. You get to this moisture level by controlling the rate of whey expulsion. Three factors contribute to whey expulsion rate: agitation (curd collisions), curd size (larger curds expel slower), and heat (higher temp leads to faster syneresis). You have to balance all these along with the starter amount and acidification profile of the starter to get the right moisture level of the curd when you drain
at the right acidity. The rate of syneresis is also influenced by the protein to fat ratio, and the strength of the curd based on when you cut from the time you add rennet. It is only in the last part that the floc is helpful.
Milk differs throughout the year in terms of the amount of protein and fat it has. This ratio of protein to fat determines the final fat content, and the rate of whey expulsion, because higher fat curd is slower to release whey (think of how slow stilton releases whey).
So there you have it. Sailor's right, a 3-4x should be a good starting point. But keep the other stuff in mind, too.
