I used to live next to a busy railway line and a motorway. It was the noise that got me down mostly, but also the vibrations from freight trains meant the tiles on the roof tended to work loose, and we kept getting leaks. Before we got used to it, the shaking would wake us up every night at about 2am.
The vibrations also caused cracks in the walls and every now and then light switches would just fall out because of this. It would have been more depressing had it not been a rented house and therefore not my problem.
A final concern, if you have children, is that they might manage to get onto the line. Railway tracks have a weird attraction for some kids and they go to extraordinary lengths to get onto them.
I'd hazard a guess that a tube line wouldn't be so bad as they're lighter, not suitable for freight and they don't run all night.
I've also lived under electricity cables. I would not be in the least concerned about any direct harm from these as, tbh, the electromagnetism from the Sun is way stronger than anything from a pylon. It was depressing though, so I wouldn't live under one for that reason. Or maybe it was just because it was in Stevenage?