The best balance of price vs function for 11 speed drivetrains. If you're running 1x11 or 2x11, you almost certainly want the medium cage (GS) version.

Deore XT Shadow+ Dyna-Sys11 11-speed rear derailleur delivers reliable and precise shifting with a stiff and lightweight open design.
Shadow+ features a super low profile design that reduces the risk of damage from trail side hazards.
The Shadow + chain stabilizer tension can easily be adjusted externally via a hex key.
Shadow + is Shimano's name for what we call a clutch, Shadow + uses a chain stabilising switch that when on will reduce chain bounce in rough terrain, maintaining more stable drive and shifting. This can be switched off to remove the wheel.
Shadow design slant angle has been optimized for use with 40-46T sprockets.
Direct cable routing prevents snagging from any trail side hazards.
Four fluorine-coated link pin bushings make this one of the slickest shifting derailleurs on the trails.
High rigidity wide outer link braces the pulley body to increase pivot joint rigidity resulting in a crisp shift.
Strong return spring for a positive shifting feel.
Durable sealed bearing pulleys.
Maximum largest sprocket:

GS (Medium) range: 42t (2x11). 46t (1x11)
SGS (Long) range: 40t (3x11), 42t (2x11). 46t (1x11)

Weight:

GS: 271g
SGS: 275g