Hi Pete, I agree with your comments about the MSc vs the MBA and am facing a similar dilemma. I have 14 years experience as a business analyst / project manager / consultant. I am currently a self employed consultant.
My prefence would be to choose an MSc (a specialist degree), but the market definately favours the MBA, especially from a top school. My feelings are that an MBA is still a general degree and usually undertaken after specialising in one area of study.
I think you need to decide what you want to do first. Which kind of company and industry you want to market yourself (for example investment banks prefer MBA's, engineering firms may prefer MSc's). Which kind of consulting organisation you may want to join and in what capacity (different roles require different skills and academic qualifications). What area of speciality you want your career path to go?
Good luck with your choice.