Considering a move to Southampton, Cardiff, Portsmouth, or London. Would like to live on coast but would like to be close to entertainment.?

Cost of living--especially housing/residential--is a factor. Are any of these places struggling more than any of the others in terms of economics, crime, or otherwise?
Update: Please recommend one or list in order of what would be best. I will need to commute, probably by train, to Oxford several times a year and would like to be less than two hours from there. For this reason, I could even live in Scotland or Ireland, if favorable.
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