1) Read REF 2014 CS reports of each to get a feel of what the faculty is up to
2) Unless you plan to get really involved in side projects meeting people in the tech scene in London (while still getting at least a 2:1), I would not put too much emphasis on the benefits of going to QMUL
3) At the end of your degree, when you're applying for developer roles, what you've done outside your degree is going to count for a lot more than the respective university's 'connections' (barring organised placements at big names)
Source: experience of London/milkround process, own research, LSE graduate landed decent job, quit after few years to get into CS
TL;DR enjoy your undergrad - go where you'll be happy so you can focus on building a strong resume, networking relatively overrated for dev roles