Almost all of the combat units are in the Guard. The Reserves are mostly combat support and service support units. National Guard units are only in the 50 states plus territories (Puerto Rico. Guam and US Virgin Islands). There are a few Reserve units in Europe and Japan as well as US states and territories. Guard units tend to be in more rural areas. Reserve units tend to be on military bases. These locations are becoming less segregated and some Reserve and Guard units are actually co-located.
Only the National Guard has Special Forces units. Only the Reserves have Civil Affairs and PSYOP units. The Guard is about twice the size of the Reserves. Pay and benefits are the same. Many states offer ADDITIONAL benefits to members of the Guard in their state for tuition to state public colleges. In addition to being mobilized for federal missions, Guard units can be activated by the Governor of the sate for assistance in emergencies (floods, riots, fires, etc.). When Guard units are under state control, they can also be "deputized" to perform law enforcement missions. This is generally prohibited for federal troops.
You can also transfer between states and between the Guard and Reserve units. Retirement will combine all your service --active, Reserve, and Guard.