It's a difficult question OP. I'll just share my experience.
tl;dr - it depends on how much money and free time you have really.
There's no other city like London, except for maybe New York. It's a metropolis. I still feel the buzz stepping off King's Cross. Lived there for uni and a few years after. My student life (and first job) in London was great! I was skint but made the most of everything on offer. Student discounts, daytime trips to blissfully quiet museums etc, free poetry readings, queueing up in the morning for West End day tickets for a tenner. All the little secret places.
However as I got older, it was no fun working crazy hours to get ahead, moving between shitty rentals. Met lots of new people but didn't make any lasting friendships. Most people around me were happily spending... meals out and drinks. 'Free things' often rammed and in any case, I seemed to be the only penny pincher in my social circle. Uni friends and I drifted apart, spent a lot of time commuting anyway.
I was drained by the time I left for Manchester. I intended to return to London but surprisingly found myself very happy here. Married with a home 20 mins away from the city centre by public transport, lots of friends and social events, and £££. I eat out , travel etc a lot more 'cos all my money isnt' going to a landlord.
It's what you make of it really. Things that sound great on paper may not be so in real life.
Who knows? I may return to London one day. In fact I go there for work sometimes, so did my DH. But unless I suddenly become career driven enough to afford what I have now within an easy commute... probably not. LOL. Maybe when I retire I'll sell up for a little London flat.