Genuine open question, which is better?
Of the pictures you've attached, personally I would say the (not very neutrally / unbiased-ly titled!) 'Huge ostentatious edifice of bricks and mortar'.
The first, bare minimum, is bare minimum at the tunnel entrance but has a large area fenced off around the entrance with utilitarian gray fencing , the sides of the cutting haven't naturalised with any grass or shrubs so it looks like a builder's yard at the tunnel entrance. Not pretty. The last one, painted concrete, again has a tunnel with the bare minimum but its hidden behind the clutter of the OHL system, with some painting as an afterthought. Looks like a token gesture to do something cheaply with a large blank area of concrete - build it to minimum cost and get a tin a paint at the end.
Both the first and last are purely functional, they're tunnels but nothing more with no effort made to incorporate any art or design into the construction, no one is ever going to look up the designer or architect of those two. The middle one, with the bricks and mortar, the designers have tried to give the tunnel some presence, some hint of grandeur by framing it as the grand entrance to something important.
And that last bit probably is the key, when these old railway tunnels were built they were something pretty amazing and important. They were the grand engineering projects of their day, those tunnels were linking great cities with a revolutionary form of transport transforming the country, built by new stock companies building out their network. Modern railway projects don't have the same significance.