This might sound stupid, but when I’m facing a difficult choice I always do like this:
1. Make a list of different aspects of the two possibilites (location, friendliness of supervisor, job prospects, research theme etc. include everything you can think of)
2. Give each aspect points according to how important they are (for example, if you don’t mind where you’ll live, you give that 1, research theme is really important, give it 5 etc.)