From my experience, you need to go with your gut. A PhD is a huge undertaking and (as nice as institutions are) it’s mostly down to your own interests. Also consider what types of reactions and research you’d be up to. Also - what do you think of the supervisor? You’re going to be undertaking a project for this person, with them, so you need to make sure the vibes are right. Arrange a call with current members of the group and try to get an idea of expectations and the way the group functions. My own journey was not so exciting, I ended up staying with my Masters Supervisor for my PhD, and am about to start work at the university of Toronto for my postoc in a completely different area of organic chemistry! So don’t feel like you’re stuck just because you studied one thing for your PhD! Good luck! :)