You correctly identified that opportunities outside the class room add value to your personal and professional development. Check about career fairs for development (NGO, government and private sector). There is one in London with various vendors, but you need to register. i would also ask about guest speakers from target orgs, a decent MSc should have a mix of academics, government officials, NGO workers and journalists. Some unis offer a panel discussion of development experts. Normally the department or career office organise speakers. Some modules are purely academic with essays/exams, others have a practical project management component: group work, presentation and real life task such as writing a grant proposal for a NGO with given guidelines. Apart from modules, see career office about skills work shop.
I think your skills are important too. It is not all about London. Some graduates from MSc Development outside London land good internships and jobs. See Oxbridge, Sussex. I would suggest to go for 'fit' and can you afford London cost of living? Each programme has certain strengths such as research groups, concentrations, fields. So my key question to you:
What are your academic areas of interests, professional goals, do you prefer academic modules or more practical training?
KCL is recent entry to Dev. To my knowledge KCL does not have a core competence and it has changed the syllabus with new lecturers. KCL positions its Development courses btw environment (water, sustainability) and its more practical Leadership and Development. I visited LSE, SOAS, UCL and KCL. For my areas, LSE and SOAS have the best development vibe in lively class room discussions and various experts. I think if your undergrad is non-development, you may benefit from some core development modules. The leadership course is more useful for people with development undergrad.