Stupid question. Running Mage Hunter with Fire, get to Homestead and now have to decide which faction. Based upon their short speech, it looks like “warriors who wage battle with Physical, Fire, and Lightning” is the one I need to pick.
Any problems?
Seems to be the obvious choice in your case, but most of the time it does not matter. Sometimes you realise later the other faction has an augment, which you would like to use… :undecided:
Personally I find the storyline of Kymon’s Chosen better than the one of the Order of Death’s Vigil, but your mileage my vary. 
I agree with the storyline bit. Bit I straight up dislike them crazy zealots. 
EDIT: From a pragmatic PoV, what I suggest doing is building what YOU think your end game toon will look like, and look at the augments needed to fix your resists. For me, the decision to side with either death’s vigil, or the bible-bashers often boils down to whether I need to use the demonbane (vit/chaos res) augment, or the spellward (lightning/aether res) augment.
Kymon’s Chosen would have the better gear for the Mage Hunter (with Kymon being an ex Inquisitor himself, and their gear focussing on lightning and fire)
https://www.grimtools.com/db/faction/kymon’s-chosen/items
at lvl 35 and 70 they provide good greens that might help you gear and their augments and consumables are good for fire as well (in particular the +50% fire pot).
Death’s Vigil only really has
https://www.grimtools.com/db/items/517
as a relevant item to you. The rest focusses on cold and vitality.
Both factions sell the same recipes.
At max level there is no real reason to have either side (you have access to better pots and augments) - in which case you might want to choose story line.
The new expansion suggests we are to explore both story lines deeper - but who knows who has the best story line or whether the story line is bound to either faction.
Honestly I’ve never come across a time when I actually needed items offered by either faction because by the time you can use them you have already gotten to better choices later in the game. Not to mention its so much easier to level other main storyline factions.
ODV every time just because of fashion alone, let alone the religious fanatic thing.
I find one of the Kymons Consumables handy. Its fairly build niche, though.
Kymon`s Tincture:: on my burn-stack guy with 2000% burn, it stacks on 7k burn for a long time on bosses and is a nice little 30K fire finisher when clearing through some of the packs of heros. Its radius is decent for pack destruction and it has no mana cost.
Infernal dust: I do use it on rings currently at end-game, but it is not essential and iirc at mid-game and mid-gear I probably needed to put other resists on the rings.
Kymons sacred oil(+50fire): Sometimes Ill start a big combat with it just because I can - but its not great and I dont hotkey it. Although if you did hotkey it, it has no CD (I think).
I havent used any of the other Kymons faction gear, though. You can find green and blue stuff that does the job as well. OR other faction gear such as Legion. As said, critical BP are avail on both.
I find Chaos/Vit to be a slightly better augment than Lightning/Aether, since the Malmouth aether pot gives 25% resistance with no CD, making chaos resist slightly more scarce than aether, and it’s easier to get elemental/lightning resist than vit.