Ride it all with Shimano's SLX Shadow 10-speed rear derailleur. The radical design means that the Shadow is super-low profile; it barely protrudes more than the quick release nut. Direct cable routing fires off shifts super quick and reduces the chance of the cable snagging on roots and rocks. A stronger spring keeps the body more stable when blasting through technical terrain at speed and yields a firm, crisp shifting feel. Plus, the bracket axle keeps the derailleur body from contacting your chainstay and reduces chatter so you just concentrate on the best line.
An important part of a rear derailleur's job is keeping the chain taut as you change gears. Chain-wrap capacity is a number that tells whether or not a derailleur will be able to do this on the drivetrain you plan to use it on. Calculate chain-wrap capacity with this formula: Chain-wrap capacity = (large chainring - small chainring) + (large rear cog - small rear cog). Example: 44/29 chainrings and a 11-28 cassette: (44 - 29 = 15) + (28 - 11 = 17) = 32-tooth chain-wrap capacity.