Dilemma

I've been offered two PhD positions and I can't choose between them.

Project 1 is in the Department of Pathology and is essentially a continuation of the MS work that I'm doing now. Since the results of my experiments came out, my supervisors have been really excited about how *significant* they are in terms of the data completely proving something that others havent really paid much attention to. They have requested that I remain on project to complete the work. I get on well with everyone that I've worked with this year, but the problem is that my staying is dependent on receiving a scholarship - they don't have enough funding to offer me one outright. In terms of receiving first-author credit in journals, this is probably better because we know what needs to be done.

Project 2 is in the Department of Anatomy and is similar to what I've been doing, except that the point has been proven and is therefore looking to explain a mechanism. There's plenty of cash and they've got enough money to offer me a scholarship, but its in an area i dont know (Diabetes-related blindness). In terms of techniques and broadening career options, this is probably the better option. The head of the lab is also a "proper" researcher in that she's not employed by the University to be a full-time lecturer and there's plenty of people around to ask for help.

So how do I choose?