I live in Bournemouth myself and know people who are go to Bournemouth uni, I myself am going to Sussex university this year to study Media or Media and Cultural studies. Lots of old people don't live in Bournemouth, it's a young people city, however some areas are rougher than others but where the campuses are, it's all safe and you have the train station, supermarkets, clubs, gardens, the beach and the high street all together. It's hard to get bored in Bournemouth and it's a lovely place. There's a lot of young people there, as well as international students.
I think you need to weigh up your options not with the surrounding area, but with what will interest you the most. Bournemouth is okay for clubbing, it depends what kind of person you are, plus you have the beach which is great and a big town to explore. Sussex is great because it's in a beautiful place and you have Brighton and London and Leeds is very vibrant too, so you've chosen good places to go. Edinburgh is amazing too.
However, you need to ask yourself which course would be better. Usually the universities will send you a little booklet which tells you what you will study throughout your time there, if they haven't done that, request one? Sussex sent me one today that tells me what's on the media course and I'm not keen on any of the electives or anything, so will probably change to Media and Cultural studies as soon as I get there. So you never know. However, Sussex allows you have to electives, as in, you can study stuff like languages among other things. You're not restricted to the one topic, if you want to take electives in other subjects, you're allowed too even though they're not listed, you just speak to your lecturer or email the university beforehand and they stick you on the other courses. Which I think is great because university is about learning new things, especially for thousands and thousands of pounds a year.
The Edinburgh one sounds good, it depends how worried you will be about the debt. Remember you don't start paying it back until you start earning 21 grand a year and only then do you pay about 8 pounds back a week. If you're really not keen on the debt or even want to go travelling after university, then maybe Edinburgh is best for you. I want to go travelling after university despite the debt, it really doesn't make a huge difference, it won't always mean you're out of pocket, it's a whole separate thing that just starts taking your money once you're ready too financially.
I think deep down you know which one you will go to. Bournemouth is great for new students, but does get boring. Not all of them are interested in just partying, a lot of intelligent people go there. Sussex you get a HUGE mix of people. Leeds as well is good for both. Don't go for the people though, or the area, go for the course. Try listing the pros and cons for the course first, before everything else.
I hope this helps. Message me if you want more information.