Some ICs like chaplains or special characters (I'm looking at you Dante!) have to suffer a predetermined PW type that don't match too well with what they're meant to do but these few exceptions aside you're pretty much free to make your choice.
Power Weapons typesFirst things first, these are the new power weapon profiles:
|Power lance||+1*/User||AP3*/4||*When charging|
The ubiquotous Power swords are the best proxy with the 5ed PWs, with the important caveat that they don't cut 2+ anymore. But they still strike an the user initiative and have no effect on the strenght.
Power axes are now mini power fists with to their +1 strength and being AP2, and same as the PFist they are unwiedly. For MEQs this means wounding other MEQs on 3s (instead of 2s) and not being able to cause instant death. Think of this as a poor man's PF and you can't be wrong.
Power mauls are rapidly being associated to the crozius arcanum the marine chaplains are equipped with. They give a phenomenal +2 to the strenght and swing at normal initiative, however the AP4, well sucks. What's the point of a power weapon that doesn't cut through the arguably most often used armour in the game? well at least you wound MEQs in 2+. Against GEQs and eldars the power maul is devastating, as a maul will munch their armour and instakill most ICs.
And we come to the unexpected guest. Power lances are a rare sight in the game. How often do you come across Rough Riders? hopefully not very often, and if you do, you might want to find new opponents. Power lances are not impressive when charging and are rather bad when they're not, so best leave them at home if you can.
What are they best used for
|No need to spend extra points on a PF when there's a power axe at hand|
Something else to consider is if you want to pay for a Power Fist when a Power Axe is also AP2. Yes the axe won't instakill marines but in most cases will wound in 2+ and bypass any armour saves, which is what you really want them for: the ability to hurt all armour types. A lot of 2+ toting rivals will still strike at the same I1, and those that don't will usually be more expensive and you shouldn't be in CC with them anyway.
There are a few units blessed with energy weapons (Sanguinary Guard and Grey Knighs Strike Squads come to mind). Adding one or two power axes amongst the power swords will give you a good balance between AP3 / normal initiative attacks and a few AP2 I1 swings.
Generally speaking, squad leaders should be left with little additional wargear, save cheap additions like melta bombs. So as long as power weapons go, I wouldn't really give them one. On the other hand, most ICs are going to be in challenges and will need some offensive power. This is due to the challenges mechanic.
Challenges and power weapons
|Runic Axe FTW|
On the other hands, assault oriented HQs/Elites will require the adequate wargear to fulfill their role. Depending on their armour and initiative you might want an AP3 Power weapon (or lightning claw), or a AP2 Power Axe (or power fist).
When equipping ICs there's a third variable to be taken into account, aside of initiative and strenght: who is the IC fighting with. Take for example a wolf lord. He's got I5 and will be joining a unit. I wouldn't waste his I5 with a power axe as another unit member can carry that axe or PF instead. This means the Wolf Lord will only have an AP3 weapon, so what happens if he gets in a challenge with a 2+ toting IC? well simply don't put him. If you are charging, set up the assault so he doesn't end is movement engaged with an enemy. This means he can't be challenged and then in his initiative step can move these 3" and engage the enemy.
ICs like Mephiston on the other hand... well he's just got an AP3 weapon and can't join any unit, so just make sure he's facing the right opponents. AP3 is not bad per se, just has a different usage to AP2.
Power weapons are versatile and affordable CC weapons that need to selected carefully, based in what your army needs and can do. Squad leaders are typically best left with little additional wargear as they're not there to win you challenges. ICs on the other hand will likely get in a challenge and need to be prepared for it. An AP3 power sword allows to attack on initative and hurt many units, while AP2 has the I1 tax.