Despite really loving London (and having lived here the whole of my adult life) I moved out three years ago & think it was a great decision. I still work in London so am one of the many commuters coming in by train - again, my job is very London focussed so it would be difficult (but not impossible) to fully break away.
I think commuting in offers quite a decent compromise as I get to live in a nice house that I own (well have a mortgage on), loads of nice local pubs & rarely have to stand in them, minutes away from quiet country lanes for cycling yet still have everything London has to offer on my doorstep.
The down sides are of course that the commuter towns can often be a bit grimey (though not really any worse than London) & I have to commute by train for the first 25 minutes of my journey (at a cost of £400pcm). So swings & roundabouts I guess.
In terms of places to move; I first moved out to Marlborough which is a really lovely/posh small town in Wiltshire. It was perfect in almost every way except it didn't have a train station so I had to drive to a nearby village then get a 2 hour train each way - that length of commute turned me into a zombie so we had to move.
Now I leave in Reading which generally has a reputation as being a complete sh!thole but actually isn't that bad and I think is quite fun to live in. It's the cultural & economic hub of Berkshire so there's lots going on. I know Reading, High Wycombe (previously lived here too) & Hemel (there quite often seeing friends) quite so would say that those three commuter towns are generally quite similar - often a bit grotty in the town center but become really nice 10/15mins out.
When I lived in Marlborough we visited Bath, Bristol & Swindon quite a bit. Don't go to Swindon. If you were fully moving West I'd pick Bath over Bristol every time - people often go on a fair bit about Bristol (probably due to some London-eque industries being based there now) but I've honestly never found it that great, it's ok though I suppose. Bath is substantially nicer & has most of the same stuff happening.
If I were moving elsewhere in the country I'd probably go for another city (the towns really are just a completely different lifestyle) - I've liked Manchester every time I've been there so that would probably be my first choice (and also probably the only other option for my job). I used to live a few different towns in the midlands so went to Birmingham/Wolves quite a lot, I most definitely would not move to either of them.
Other than that, I think I'd look at moving country (especially given the way things are going here).