Electricity Assault - A combination of so-so melee attacks and so-so ranged attacks. Unfortunately, it lacks a lot of the best electric melee and electric blast attacks.
Energy Assault - This set has some of the better energy melee single target attacks, but unfortunately forces you to take the nearly worthless power bolt as your first pick. The utility ability Power Boost synergizes very well with the Dominator's control sets.
Fiery Assault - The real tragedy of this set is the requirement that you take the absolute garbage power Flares. I have no idea why the developers did this when almost everyone despises that power from the Fire Blast set. It also gives you Fire Breath instead of Fire Ball. The power choices in this set are dubious at best.
Icy Assault - Again, this set hits you with the terrible starting power, but after that it isn't bad. It has a decent amount of AoE damage and Chilling Embrace slows incoming damage significantly.
Psionic Assault - This is one of the more popular secondaries for dominators due to the exotic psi damage type, and the final power is a massive, huge radius PBAE (Point Blank Area Effect power). With domination, Psychic Shockwave is a vicious killer.
Thorny Assault - With many powers borrowed from the scrapper spines set, the attacks have slow animations and lackluster damage.