Each of the three major Ordos of the Inquisition have an HQ choice (along with a special character) in the Grey Knight's codex to represent them. While all three are similar, they do have different choices and thus, I'll cover them in separate (but shorter) posts. First, I'll start out with the Ordo Malleus.
Ordo Malleus Inquisitors are meant to be specialized against Daemons and can be taken in either a Radical or Puritan. However, unlike the older codex, your Inquisitor choices do not affect what units you can and cannot take; a Puritan can take Daemonhosts and a Radical can take Grey Knights in the army. Let's go onto what the Ordo Malleus Inquisitor has by default.
The Inquisitor starts out with Frag, Krak, and Psyk-out Grenades, Carapace Armour, Bolt Pistol, and Chainsword. He is also an Independent Character with Stubborn, which is conferred to his squad. While his subpar statline (aside from 3 Wounds) would make him seem like an unattractive choice, he can take a lot of extra equipment and unlocks the Henchmen choices. Henchmen are the major part of taking an Inquisitor, but I'll cover them in a later article. Let's move onto the options.
Power Sword - With only strength 3, chances of this being a good choice are low. Even with Hammerhand, you are better off either avoiding close-combat or picking up a Daemon Hammer, and you should definitely be picking up Terminator Armour if going for close-combat.
Plasma Pistol - While having the plasma shot is nice, I'm not sure if one shot (generally the best you will get a game, if even) is worth the points, especially seeing how this is a close-combat oriented weapon at which point you'll be picking up Terminator Armour.
Combi-weapon - Combi-Melta is probably your best choice here, if you choose to take one.
Power Fist - Utterly worthless as the Nemesis Daemon Hammer is superior for the same cost. It's just here for modelling purposes.
Incinerator - Incinerators are pretty strong, and the Inquisitor is a nice spot to take it. You can't really focus on close-combat and take an Incinerator, though, so you will probably fire once and either assault or die next turn, sadly. Still a nice choice.
Nemesis Daemon Hammer - A good choice for close-combat oriented Inquisitors. You get this for "free" when upgrading to Terminator Armour, so you may as well just pick up the armour.
Daemonblade - A weapon which seems quite fun to use despite being a bit random. I'm not sure as it is very competitive, as the most likely roll of a 7 also happens to be the worst and doesn't count as even a Power Weapon without taking a specific upgrade (either as a Force Weapon or a Etherblade).
Hellrifle - Essentially a Strength 6, AP 3 Sniper without Pinning. Seems like it would be another fun weapon to use, but you would have to be in a squad that would be well fit for it, such as some Jokaero Henchmen.
Servo-Skulls - You can take up to three of these for a low point cost. Good if you have a lot of Conversion Beamers or other blast templates or if you plan on attempting Deep Strikes often. They do offer scout/infiltration defense, too, so a good left-over point spending, but they don't make you more combat effective. They are cheaper here than taking them on a Grand Master.
Psybolt Ammunition - An extra strength on bolter shots is nice, but if you have Terminator Armour you will probably be taking a Psycannon and otherwise you don't have an amazing bolt-weapon anyway. A decent upgrade if you have floating points.
Empyrean Brain Mines - A decent option, especially if you have a Daemon Hammer so that you can attempt to stop your enemy from striking you down before you strike. It is slightly expensive, so I wouldn't say it is anywhere near an auto-include, just a point sink.
Power Armour - A fine upgrade, but the awkward point cost of 8 will probably mean you will have 2 points "floating" at the end of your army list and if you need the extra Armour, you might as well pick up Terminator Armour. Not a bad choice, though.
Terminator Armour with a Daemon Hammer and Storm Bolter - A really good choice, despite the price, as it allows you to pick up a Psycannon (a relentless one, at that) and gives you an Invulnerable Save and a good close-combat weapon. One of the main things I would look at for an Inquisitor.
- Psycannon - Psycannons are amazing weapons and are the best weapon you can pick up on the Malleus Inquisitor, warranting taking them alone. You can only take them with Terminator Armour.
Psychic Mastery - A fine upgrade if you are putting the Inquisitor into close-combat (for Hammerhand) or if you want to be able to control your reserves well with a reserve based army (with Psychic Communion). Note that you do not have to exchange your current weapon with a Force Sword due to Errata in the Grey Knight FAQ.
Close-Combat Oriented Ordo Malleus Inquisitor - (105)
Terminator Armour, Combi-Melta, Hammerhand
Adds a bit of a punch to close-combats with an extra Hammerhand cast, a Nemesis Daemon Hammer, and a good armour/invulnerable save.
Shooting Oriented Ordo Malleus Inquisitor - (80)
Terminator Armour, Psycannon
Great to add to a squad of Purifiers with Psycannons on foot, Purgation squads, or Terminators
Non-Terminator Shooting Oriented Ordo Malleus Inquisitor - (40)
A cheap Inquisitor just to grab an extra decently strong shot and when you can't afford or can't place (due to Terminator Armour) the Psycannon built Inquisitor.
Keep in mind while none of these seem particularly attractive, the main reason you take these HQs is either for a cheap HQ slot so that you can focus points elsewhere or so that you can take Henchman.
Next post will be very similar but instead covering Ordo Hereticus Inquisitors.