I am going to buck the trend.
First off, the conversions are excellent, really lovely tones, nothing blocked or blown. You have captured the scale really well, and the 'railway' atmosphere.
#1 seems to be the favourite, but for me the distortion is just too great on the right hand arch, and the cottage is leaning too obviously.
#2 the comp is just a bit too tight.
# 4 is really good, nice composition giving a super sense of the scale of the structure, and the depth of the valley. However, I think the processing is too contrasty, the sky is overcooked, and there is insufficient recession in the landscape.
# 3 has a still better composition though - you can really see the landscape beyond, with lovely recession into the misty distance, placing the viaduct in its full context, and that gorgeous ray coming through the clouds in the distance. I love the RH masonry - you get a really powerful expression of the massiveness and scale of Victorian railway architecture, and the close-in wide angle effect gives a sense of the dynamics of the steam trains passing over. The processing is superior to #4, much more natural, less forced.
So #3 easily. I bet it makes a far better print than #1!