Faction: Sith

Top Tech Pieces to Know:

Dark Force Nexus (Force battery, Summon, Presence of the Dark Side)
Sith Holocron; Exar/Freedon/Marka ghosts (Force batteries)
Queen Amanoa (Shooter defense, out-activation defense)
XT-6 Droid (Activate an extra character in a round)
Sith Recruit (Self-Destruct + reroll option)
Sith Ordnance Specialist (a Sith Recruit with Satchel Charge)
Sith Assassin of Malachor V (Levitation)
Darth Bandon (+10dmg vs adjacent)
Prophet of the Dark Side (Charging Assault +10 to non-Uniques)
Juggernaut (110hp bodyguard with armor)

For most of these strategy guides, the top pieces to know are the tech pieces. The CEs and other tricks that boost a squad and move people around. Then each faction has its own (larger) set of viable offensive pieces. Sith are quite different. Some strong tech pieces are listed above, but this unlike other factions, they rarely define a squad. Sith squads often revolve around a big (50+ cost) Sith piece or two. Each works differently, and you build around those pieces (e.g. using the above tech pieces to fill in for the big bad's weaknesses), as opposed to starting with the key tech pieces and building from there like you do in many other factions.

Top Big Sith Pieces (cost 40+):

There is a lot of subjectivity on what the top pieces are but here's a sampling:

Darth Caedus, Sith Lord (Sith Battle Manipulation and Master Illusion; pairs well with Barriss Offee, Rogue Jedi)
Darth Plagueis, The Wise (Chain Lightning 4, Damage Reduction 10, Soresu Style)
Darth Revan, Sith Lord (Self-swapper)
Darth Bane, Sith'ari (All-out offensive monster)
Lord Vitiate, Sith Emperor (Presence of the Dark Side, Opportunist to non-Unique Sith followers)
Darth Cognus (Twin, Surprise Attack, Evade/Parry. Needs a Force battery)
Darth Traya, Lord of Betrayal (Creates a Sith Triumvirate subfaction with Sion/Nihilus)
Darth Vader of Scarif (Scissors-style beatstick)
Sith Battlelord (+10dmg and Double Attack to non-Uniques)
Sarasu Taalon (Cornerstone to a Lost Tribe squad)
Darth Zannah (Soresu Style Mastery)


Top Mid-cost (20-39) Sith Pieces:

Atton "Jaq" Rand (Override shooter)
Lord Kaan (Thought Bomb)
Ommin, Sith Sorcerer (Emplacement with Presence of the Dark Side)
Sheev Palpatine, Sith Apprentice (Force Attuned with Lightning, Lightning Assault, Force Dash)
Sith Saber (Twin attacker)
Skyborn Ranger on Uvak (Battering Charge +20)


Subfactions:
Gloom Walker
Lost Tribe
Sith Triumvirate


Some squads:
Dance of Death: Ubertank (2015 GenCon runner-up)
Lord Krayt + Darth Revan, SL (2013 top 8)
Plagueis and Cognus
Lost Tribe
Sith Triumvirate
Sith Battlelord & Lord Vitiate



ATTA/RoS newcomers:
Darth Bane, Sith Master boosts Darth Zannah or another ally through Rule of Two and packs a huge punch of his own.

Githany is a 27pt Twin attacker that introduces the Brotherhood of Darkness subfaction.

Sith Eternal Trooper has GMA but only one attack, so he can make great use of Double Attack from the Sith Battlelord. Exclusive Loyalty to Sith means you can't boost him with Fringe pieces or do much with him in an Imperial squad.

Sith Tyro brings Lying in Wait (a limited defense against initiative control) to Sith.

Sith Eternal Emperor is Palpatine from Rise of Skywalker. Sith Battle Manipulation along with Force Storm 4 and Drain Life 5 (high Force, high damage abilities).

Also worth metioning: Pryde, the Jet Trooper, and Treadspeeder from the Imperial faction can all travel to the Sith faction as part of the new Sith Eternal subfaction.