Mentioning that exposes the fact that the S and D closing, plus that of the M and SWJ, plus the DN and S, was, now in hindsight, way over the top when considering north to south traffic. One should have been retained. My vote would have gone to the M and SWJ probably -it's a big subject though.
I thought this was a fascinating question (I was tempted to put it in infrastructure rather than Nostalgia, but sadly, nostalgia is probably the place for it to be).
Supposing the powers that be had taken a more strategic and long term view of links from the Midlands to the South Coast, and decided that we'd needed to retain one or more these North to South routes. Which of these regional railways would have been the best to keep.
We have:
S&DJR linking Bournemouth and Bristol via Bath Green Park
M&SWJ linking Andover and Cheltenham via Swindon
DN&S linking Didcot and Winchester via Newbury.
My choice would be the S&DJR, and that's not just because of the Nostalgia value and it's advocacy by the great Sir John Betjamin.
This is because although the intermediate settlements aren't huge, many of them such as Wincanton and Blandford are isolated from the network enough to have generated a regular passenger traffic that would have perhaps justified the routes existence as a basic railway through the lean times. Additional to this, it has the large conurbations of Bournemouth to the South and Bath and Bristol in the North, which as well as generating a through traffic to keep things ticking over would have led to commuter flows at east end.
With regard to the DN&S, it's main settlements are all on existing routes, and it's hard to see how a reasonable through traffic could be generated. On the face of it, had it survived, it looks as though it might have had some sort of future as a freight route (particularly had the Great Central from Banbury survived), but even though it avoids Reading, I think the sections south of Winchester and North of Oxford would have constituted pinch points negating its value as a freight relief route.
So to the M&SWJ. When taken together with the Southern Railway route from Andover to Southampton, this would have been a better candidate for modern freight route, providing a path from Southampton towards the midlands away from the mainlines of the South East, and it would have provided a passenger link to some important towns such as Marlborough and Cirencester, yet I'm not convinced the route would have generated the right mix of local and through passenger traffic through the lean times. I'm also not sure that Cheltenham would have been enough to generate commuter traffic on the Northern end of the line. Perhaps this is one of those routes that should have been protected.
My vote defenately goes with the S&DJR.
Any other thoughts ?