balanced connection, better than single ended?

If you have gear that can do balanced & unbalanced connections which is preferable and why? I have read that balanced connections are better for long runs of cable otherwise a single ended connections are fine but not sure of this since I have yet to use this sort of connection. Also I read that some gear is not truly balanced in their circuitry thus this gear may not benefit from a balanced connection. I ask only because I'm recently buying an amp that has true balanced circuitry but now must find a preamp of the same.