Here's the most popular ones and their uses. Whichever looks most appealing you should take.
Fireknife (Plasma Rifle, Missile Pod, Multi-Tracker) - Most popular and most versatile combination, Good at killing heavy infantry, low save models, and light vehicles.
Death Rain (Twin-Linked Missile Pod, Flamer or Target Lock) - Good at killing heavy infantry and light vehicles, and is accurate.
Burning Eye (Twin-Linked Plasma Rifle, Flamer or Target Lock) - Good at killing heavy infantry and low save models (like marines)
Sunforge (Twin-Linked Fusion Blaster, Shield Generator) - Good deep-striking suit. Can get behind tanks to kill them, and is pretty hard to kill thanks to 4+ invunerable save.
Death Rain Fireknife (Twin-Linked Missile Pod, Plasma Rifle, Hard-Wired Multi-Tracker) - Better version of Fireknife, but usually only used on Shas'el commanders, as it is expensive.
Burning Eye Fireknife (Twin-Linked Plasma Rifle, Missile Pod, Hard-Wired Multi-Tracker) - Better version of Fireknife, but usually only used on Shas'el commanders, as it is expensive. The Death Rain Fireknife is usually used more often than the Burning Eye Fireknife, as the Missile Pod is more versatile and destructive.
Accurate Fireknife (Plasma Rifle, Missile Pod, Targetting Array, Hard-Wired Multi-Tracker) - Not able to use yet. Targetting Array is rumored to be a supprot system in new codex. It makes both the Plasma Rifle and Missile Pod more accurate. Would be good on Shas'els, as they get Shas'O BS for only 5 points.