Thinking about switching to a Masters from a PhD, advisor wants a decision now
That is a tough decision, but do you think it's mainly the project or just the whole concept of PhD that isn't appealing? Would it help to switch projects or advisors? It sounds as though you have a good fit with your internship, so perhaps it would be a good to gain that work experience and, if you want later, return to school with a clearer idea of what you want to work with (as you mentioned). 

With regards to the type of job you want in the future, have you spoken to other professionals to gauge whether or not a PhD is really necessary? That might help in your decision as well. Good luck!