Welcome to Gaia! ::

Suppose I'll kick off then with my own experiences so far, having fielded one or more Knights a few times now with varying success. Despite the fear factor they carry with them, they're not as scary or overpowered as some make them out to be. One of the things I have learned by now is that Farsight is a beast in close combat and he will kill your Knight, it happened to me twice now! sweatdrop But I will have my revenge you pesky fish, oh yes I will. Also, the best way to kill a Knight is to shoot at it from more than one angle, leading to the agonizing choice of where the Knight player needs to point the ion shield and hope for the best. Good luck blocking four meltaguns coming in from three different angles!

A Knight supporting an army is good and fun, I did this three times with varying results. I also ran a list with two Knights (Paladin and Castigator) backed by Pask and two Exterminators, a trio of armoured autocannon Sentinels and a Taurox Prime filled with plasma storm troopers against my Tau opponent, which resulted in my massacring him, though he had some really, really bad rolls on his part, plus he was giving that new flying Riptide variant a whirl, which lead to him not using it properly and ending up as fodder for my Reaper chainsword. I fear there may be a rematch coming sooner or later, with him bringing his usual toys.

Currently I'm looking at fielding the Knights using the Questoris Imperial Knight list from the fourth Horus Heresy book, Conquest, which gives you a nice Knights only army list that allows you to field all Knight variants currently put out there, with some extra flavour in form of Knightly ranks that you must purchase for your models. These ranks don't just give you extra special rules, but they will also define what slot on the force organisation chart it is taking up. (So giving a suit of armour a Seneschal title would make it a HQ, giving it a Uhlan title makes it fast attack and so on)

House DuChess - Questoris Knight Crusade army - 1250 pts

HQ
Seneschal(1) baroness Marianna DuChess - 50
Knight-Castigator w. occular augmentics* - 390

Troops
Scion Martial(2) Salena DuChess - 0
Knight-Paladin w. occular augmentics & bio-corrosive stubber rounds** - 395

Heavy Support
Scion Arbalester(3) Valentina DuChess - 25
Knight-Errant w. occular augmentics & bio-corrosive stubber rounds - 390

Grand total: 1250

* Occular Augmentics: The Knight has Night Vision and may re-roll any results of a 1 on the Vehicle Damage table and Destroyer Weapon Attack table which are inflicted by their shooting attacks at a range of 12" or less.

** 36" S2 AP 6 Heavy 3, Poison (4+)

(1) - Seneschal title gives you +1 WS, BS and a 3++ ion shield save. It also allows you to re-roll on the warlord table.
(2) - This is the standard Knightly rank, with no extra benefits or bonuses, making the Knight a troops choice, hence zero points.
(3) - Arbalester makes the Knight heavy support and gives it Tank Hunters, it also gives you Skyfire if you didn't move the last turn.