depends on what you want to do afterwards and what your access is like.
rolls are easy for you to fit yourself (I think B&Q are doing a special on them at the moment). you may need a pump to put in a decent amount of sprayed stuff.
be aware that new build regs need more than 4in - i think it is 12in. Although new-build regs dont apply to an old house. the regs are there for a reason - 4in insulation is not enough. Our house was exactly as yours (14 and 4in). we put down slabs a few years ago and then pumped cellulose in around the area where the roof height is too low to walk in (20in deep insulation). The central part we left slabbed and put down floor boards so we could still use it as storage.
anon473