I've got a 55" Sony Bravia Android TV.
Pros: Great picture, built in Android so I can run media centre and any other side loadable apps and not have wires and boxes everywhere.
Cons: Android TV is a bit underprovided for, remote and TV menu have far too many useless features, Occasionally it needs a reboot like most computers, wall mounts are expensive but you can bodge something together in B&q for a out a fiver.
Cost me something like £250 from John Pye, YMMV. Not 4k but I've not got anything 4k anyway.