For maths, don't go, especially to summer/winter school, unless you are in desperate need of help. And even in that case, a good tutor will be better. The end of year revision was also quite 'useless' I re-learnt maybe three important points, it was just a session where a teacher(I got Irena) does a load of questions, and goes through their huge notes. Wasn't worthwhile in my opinion, you could learn more about your own weak points completing papers/questions.
For Business winter school seemed good at the time, but when I covered the material myself later I realised that I really did not need help...
I went to TSSM winter school, and TSFX end of year lecture. In my experience TSFX notes are better, and the actual lesson is entirely dependent on the presenter, 'luck of the draw'. It's up to you really.