What are the prospects for jobs from each project based on the techniques you have been told you will use (thats if its a science one) - i.e. there will always be more jobs in cancer, heart disease etc than in physiology based projects - again this is only science directed - but I assume it translates to a few other areas
How easy is it going to be for you to live and get on in the area? do you easily make friends?, how many other PhDs were in the department? you only have to look at previous posts to see the importance of support from close friends and other PhDs.
Finally I suppose - do you want to travel, live away from home (if you don't already)
Dundee (in a science view) has some great research going on, there is a good student population and plenty to do, plus you are never far away from Edinburgh, Glasgow, the highlands etc if you want some time out