I’m overwhelmed by the choice of tutorials: can you help me choose?

The main criterion is that you should be really interested in the field:  most students find they work more intensely than they ever have done before, and to sustain that level of effort it’s important to have a real interest in the subject matter.  The choice is really open to you, but you might like to choose courses you can’t cover at your home university, or ones which depend on the greater library resources in Oxford compared with your home university’s.  It often works well to build on topics you’ve particularly enjoyed at your home university and would like to follow in more depth.  Make sure your tutorials give you the credits you need.