Power lines as in electrical sockets and the wires that connect them. YMMV when it comes to the quality and design of the electrical system in your house. It also depends what devices you have plugged into your sockets. Any kind of AC, heater system, or really anything that has a motor can backfeed noise into the line that play havoc on the powerline signal. I say it goes Ethernet > MoCA > Mesh > Powerline > Weak Wifi in order of performance. If you can run ethernet into the room with weak signal I think that would be your best bet.