Every violinist has a different style, so it's important to be able to recognise their styles. You don't have to like everyone's style but you have to know these styles.
I don't have favourites, I think, when you play, you have to be like a prostitute, you have to love the piece you are playing. Even if you don't like it, you have to play it as if you would like it. Then you are a good interpreter.
When you can hear a violinist, that is better than you, then you learn from him, because if you play with somebody who is worse than you, then you go down.
A good interpreter can take a piece of bad music and make it sound pretty decent, while a bad interpreter can take good music and make it sound cheap. I can tell that some people have a bad taste, and unlike on the piano, they smear around a lot, that is bad taste.
Of course the most difficult thing on the violin is always intonation. The second one is rhythm. If you play in tune, in time with a good sound that's already high level. Those three are the main things.
Colour does not make so much difference. Look at the Bach Chaconne: There is not one dynamic mark in the whole Bach Chaconne. Colours do not make so much difference.
It would be easier to say, what was the difference in style from many years ago. Many years ago, the old violinists, they also had a good technique, they were not tonally as good.
So, first you have to be able to play with a metronome. Then you take your freedom. If you play in an orchestra, you got to watch the conductor, he is like a metronome, but it is more difficult because he can change rhythms.