x264 H.264 Encoding - Resolution vs Bitrate?

When encoding with x264, which is better:
Higher resolution and lower bitrate
or
Lower resolution and higher bitrate?

I'm aiming for a certain filesize and am trying to figure out the
perfect balance.
Current dimensions are 1280x720, and the bitrate is appx 9,000 kbps.
It's a recorded TV show from a TV tuner.
But I'm looking for a more general guideline.