Best Weapon Load-out For a Group of Allied Battle Servitors?

I'm looking to get some more firepower for my Imperial Guard, I was considering some of the FW artillery units but then I thought about the options Battle Servitors would bring to the table. So here are my own thoughts on the weapons and the formation, I'm hoping so of you are experienced in using them on the board and can recommend a good load-out from your experience of using the different weapons?

Heavy Grav-cannon - As mentioned this seems a solid choice due to it's sheer number of shots, probably going to take one unit of these. After all grav-weapons are the best anti-monster weapon in the game.

​Torsion Cannon - An amazing weapon on paper however the BS3 could be a deal-breaker for a 1 shot weapon?

Heavy Arc Rifle - A great anti-tank weapon, perfect for the more heavy armour that the majority of my weapons have trouble with.

Plasma Culverin - No very interested in this weapon as I already have a plasma russ plus 'get's hot' with a 4+ save will decrease it's life-span even more on the board.

Holy Requisitioner Formation - Tempting but for 3 things 1) they'd be in reserve instead of shooting, 2) They'd be closer to the enemy which can be dangerous and 3) Can't take the grav cannons.

So what are your suggestions for an allied detachment of battle servitors?

Aren't the servitors Relentless? It'd be hard to resist taking Grav Cannon in that case.

What are you fighting against most?

If you are fighting marines/monsters etc then go for the Grav. it works wonders... as Cptn Bubonicus mentions they are relentless - everything in the codex is ;)

i have found the grav versions are almost as effective as the haywire ones against killing tanks - you only need two grav glances to wreck a 3 HP vehicle, if you have a squad of 4/5 servitors that is 24-30 grav shots per turn - goodbye almost any tank etc.

If it is Demons/nids/orcs then i would go plasma culverins as a squad of 3 can put out 6 plasma blasts per turn, do not forget they have two wounds each - leading me onto the Tech-Priest Dominus.

if you take servitors - add in a Tech Priest Dominus as well, for one thing it makes a bound allied detachment, but he slices & dices with a lot of heavy fire power (keep him with basic load out except for a Conversion field - 4++ for 5points who woudn't?), and can tank the wounds on his 2+ save/4++ save and FNP keeping your servitors alive longer. in addition to this he could heal one wound per turn/repair your Russ's on a 2+ as well, if you take plasma servitors, and put him with them they are not likely to loose more than 1-2 wounds per turn at most (which would not kill a servitor as plasma wounds go on the model fireing the gun), he could repair those wounds and keep them fighting longer...

I would consider getting two boxes of servitors and a Dominus, making 50% of the Plasma, and 50% Grav and you can then mix and match - the choice to upgrade to grav from plasma is free. both Grav and the plasma work just as well (nearly) on both infantry and vehicles so it is easy to mix weapons - e.g. squad of 4: 2 plasma & 2 Grav. (or just magnetise weapons and choose each battle!)