I think this very much depends on the context, and being a good virtuoso violinist (or cellist, or singer etc) picking the right temperament for the right effect. If you're playing in an orchestra with many other instruments, you likely have to stick with 12TET. If you're playing a violin concerto cadenza, if you're playing a piece for solo violin, you likely want to play in just intonation as much as possible. If you're playing a piece for accompanied solo violin (violin + accompanying piano or orchestra i.e. sonata or concerto) then it very much depends on the moment and what sounds good for the music. Especially for an instrument like violin, which is extremely sensitive to every tiny expression performer can add, it's hard to make blanket generalizations. Ultimately, it's all about the artistic style of the performer, and composer's vision.
