Well it should be obvious who I like.
Martins are the standard of the bluegrass world.
Gibsons are the standard of all country singers.

Why is this? The pro knows. The rest are all wannabes. There are now a whole line of lower priced Martins. Gibson hasn't compromised there name yet, but a decent used small body LG or B25 series can be had for $500-$600. That, and they will never lose their value.