I'm considering QMUL as one of my choices for next year. Sorry if I can't target some of the questions you've asked as I am not totally aware myself.
QMUL is a Russell Group university, and Russell Group universities tend to focus especially on research. As with a lot of things regarding universities, these tend to be pretty pointless proxies in my opinion when it comes to how good is the specific course you're considering objectively. However, most people tend to be intrigued whenever they hear things like "Russell Group". Yes, it's not as highly ranked as Imperial/UCL, but they still do pretty decent for CompSci-oriented courses, so by name it is still a decent university. From what I've read, the CS courses are generally taught well, of course not up to par with Imperial's standards, for instance, but nonetheless. I suggest that you study the modules of the courses you're looking at and compare and contrast between your other choices. "What do you like the most yourself?", and "Do you think these modules are as important if you believe you can just learn them in your spare time?", are probably good questions to ask yourself.
Location wise, yes, a lot of people tend to have a disliking for East London and this is a pretty historical thing. I'd argue that it's "London snobbery" (in your words) to an extent. Stay to yourself, definitely watch your phone as phone theft is admittedly one of the few legitimate issues in London (although really if you're sensible you should be fine), and you won't get hurt. All areas are going to have their positives and negatives, but assuming you're going by Tube, you'll be exiting from what is just yet another busy London tube station and you won't even be walking for more than 5 minutes to the campus. The surrounding area of QMUL should honestly be fine, it's probably going to be populated especially by students and Victoria Park seems to be fine from what I've read. No part of London is so unsafe that you cannot risk entering it.
Realistically though, what do you think will happen? UCL has campuses in East London (admittedly UCL East is a very recent one) but I've never seen concerns about UCL in regards to this. All of the universities you've mentioned are still in Central London and especially very busy areas, anyway.