There are two class specializations for the Sith Warrior (or otherwise known as advanced classes). They are Sith Marauder and Sith Juggernaut.

Juggernaut

Sith Juggernauts are Sith specialized in combat endurance and were known for wearing armor that provided them special protection in battle.

Sith Juggernauts were known to primarily wield one lightsaber in combat, and were frequently adept at using the Force to cause terror and despair in enemy combatants.

Primary Focus:

• Single Saber / Heavy Armor
• Fear and Darkside Auras
• Tank or Single Saber DPS

The second specialization is the Marauder.

Marauder

Sith Marauders are Sith Warriors who fought for the Sith Empire during the Great Galactic War and the Cold War that followed it circa 3,653 BBY. They specialized in dual lightsabers and dealing high amounts of damage to enemies in melee combat.

Marauders specialize in destroying their enemy; within and without. They are also able to use Stealth.

Primary Focus:

• Dual Wield Sabers / Armor
• Saber Fighting Specialist
• Melee DPS
• Temporary stealth usable in combat

Further reading:

• Sith Juggernaut guide
• Sith Marauder guide