I have a horrendous 50ft wall what climber do you suggest

Which direction is the wall facing in?

welcome to GoY.
how about a virginia creeper, though it is not evergreen.

if its a shady wall then a climbing hydrainger would be good .we have one and once it gets going we have to cut it back quite hard so with a large wall it would be fine not evergreen but when in leaf its a lovely bright green

Remembering an earlier question, is it your wall?

And a fifty foot wall is heck of a high to cover!

As Wagger says, it is your wall? If not, beware of planting anything against it without the owners permission.