Okay, here's how I'm thinking of fielding my Witchunters in 5th edition. Basically I have dropped my usual pair of Winged Cannoness' and two units of Seraphim in favor of some allied guard for long-range tank killing and holding objectives on my side of the table, and an Inquisitor counter-assault force in a land raider.

This gives my army a balance between a very powerful long-range firebase from the Guard and Exorcists, combined with a powerful mechanized advance from the Sisters in Rhinos. The Landraider falls somewhere inbetween, advancing slower then the rhinos so as to make use of it's weapons then moving up to counter-assault any problems my Sisters Squads get into.

Thoughts?

Witchunters (2000 Points)
Models: 84
Vehicles: 8
Faith Points: 4

HQ:
Ordo Hereticus Inquisitor Lord and Retinue (9 models):
Ordo Hereticus Inquisitor with Power Weapon and Bolt Pistol. (56 Points)
3 Acolytes with Carapace Armor, Laspistol, and Power Weapon; 3 Crusaders with Suppression Shield, Carapace Armor, and Power Weapon, 1 Familiar and 1 Sage. (121 Points)
Land Raider with Extra Armor and Smoke Launchers. (258 Points)

Troops:
Battle Sisters Squad (10 models):
7 Battle Sisters with Boltguns, 1 Battle Sister with Flamer, 1 Battle Sister with Heavy Flamer, and Veteran Sister Superior with Bolt Pistol and Brazier of Holy Fire. (152 Points)
Sisters of Battle Rhino Transport with Extra Armor, and Smoke Launchers. (58 Points)

Battle Sisters Squad (10 models):
7 Battle Sisters with Boltguns, 1 Battle Sister with Flamer, 1 Battle Sister with Heavy Flamer, and Veteran Sister Superior with Bolt Pistol and Brazier of Holy Fire. (152 Points)
Sisters of Battle Rhino Transport with Extra Armor, and Smoke Launchers. (58 Points)

Battle Sisters Squad (10 models):
7 Battle Sisters with Boltguns, 1 Battle Sister with Flamer, 1 Battle Sister with Heavy Flamer, and Veteran Sister Superior with Bolt Pistol and Brazier of Holy Fire. (152 Points)
Sisters of Battle Rhino Transport with Extra Armor, and Smoke Launchers. (58 Points)

Battle Sisters Squad (10 models):
7 Battle Sisters with Boltguns, 1 Battle Sister with Flamer, 1 Battle Sister with Heavy Flamer, and Veteran Sister Superior with Bolt Pistol and Brazier of Holy Fire. (152 Points)
Sisters of Battle Rhino Transport with Extra Armor, and Smoke Launchers. (58 Points)

Imperial Guard Infantry Platoon (35 models):
Command Squad with Lascannon. (65 Points)
Infantry Squad with Lascannon. (85 Points)
Infantry Squad with Lascannon. (85 Points)
Infantry Squad with Lascannon. (85 Points)

Heavy Support:
Exorcist Tank. (135 Points)

Exorcist Tank. (135 Points)

Exorcist Tank. (135 Points)

I've read that WH are great now in 5th ed and the codex holds up really well. They have been doing pretty well consistently at tournaments My mate has an army he was going to give up on but I think I want to borrow it and play some games in the new year.

The idea of the list sounds good but I need some WH experience behind me to really pass comment. The three Exorcists sems pretty standard but from reading around it seems the Book of St Lucius is the uber-cheap and must-have wargear but you don't seem to have taken it?

The list is about 17 KPs is it?

Would a melta gun or two be worth taking for anti-tank (instead of the flamer in a couple of the SoB units) in case those lascannons/tanks get compromised early on? You'd still have another flamer in the squad.

Although i'm only just beginning to dabble into WH, i'd have to agree with Matt on the good ol fashioned 'belts n' braces' rule.. i'd use a variety of weapons which could deal with a large spectrum of enemies, just in case really.

Apart from that it's a awesome list, though I personally would have had a higher ranking battle sister officer with the battle sister squads, if anytihng to boost the faith points.

I like the fact that the list breaks the usual sister mold.

Here's the but though.

I really would swap a couple of those sister flamers for melta guns so they provide a multiple threat. and some AP1. You have loads of anti troop power already in the units.
Faith points are very low for 2000pts. You might get away with it as the main faith point hogs of seraphim and jump canonness are missing. This ties in with the melta guns in troop units. When your faith runs out, they still have something with a little punch.
I really wouldn't use the inquisitor as a counter assault unit, as you have to pimp them out to the max to make them halfway effective. They are quite frankly awful in combat. Also, what function does the sage have in the retinue? I don't see the point of having +1 BS for the boltpistol, apart from a cool model.

I made the mistake of using a pimped inquisitor with loads of cool models and wargear, but the unit was actually rubbish and achieved nothing. I focused the units role, shaved a couple of models and downgraded the inquisitor. It does better for it's points now.

I hate advocating efficiency over the rule of cool, but bloated inquisitors only disappoint, tempting you to leave splendid models in the box next time you play which is the real crime.