How to use the Forsaken depends a lot on their Disgrace, which is the stat that determines their cost. High disgrace = low cost. All of this was on the last patch and items may really change this up, I don't know.
Extreme low cost--extremely low damage. Talking 1-3 EE cost. The high number of surround turns you get on these can be used in the first days of a loop to get all Forsaken out early. If they focus on a single damage type they might be able to pay for themselves with a T0 bonus (+2 EE for core circumstance level 2), so try it. I used a PLEA-focused commander here in a loop, that had a rather insane Trauma modifier on it (see below).
Low cost (single digit, I aim for about 4EE)--low damage. So you'll need a damage multiplier to do anything useful with them. An easy damage multiplier is--focusing on a single type of damage, which is worth 1000% (10x). So your little tiny Forsaken need to be trained so that they give massive damage to one circumstance only. For similar EE, they compare very favorably to Demons with a Suppressor equipped for the same cost, since you aren't paying extra for turns or captures. Get them a lot of experience in a single type of damage. It's helpful to keep their Obedience low if that is an option for you. I don't worry too much about whether these have a bonus, but I'm not playing too deep into campaign loops right now--if I were, I'd try to eventually get Distorted Forsaken into these roles for the +50% bonus to Circ damage.
Medium cost--medium damage. These are Forsaken that cost in the 10-35 range (my most recent save used 12). I give these experience in 2 damage types. This is a range where it really is helpful to have a Distorted chosen because you can take advantage of both bonuses. Can be useful when you don't have the upgrades for multiple captures/many turns--often these are cheaper than various 3-capture basic commanders.
High cost--high damage. I'm thinking 35-125 EE cost here. I don't really find much use for Forsaken at this level, though they might be more helpful against the Superior/Animalistic Chosen, I honestly don't know. Does anyone out there use chosen in this range effectively? Can they get Orgies started with some savings over 3-capture long duration basic commanders?
Very High cost--Very High Damage, but that's not really what you care about. 125EE or more. I put these chosen into Positions and summon them only when I have one or (preferably) multiple Chosen ready for one or more T4 breaks. You can get some pretty extreme bonuses here, but since these depend on the minor/major/core of whatever Chosen show up, this may not be an option for you. The damage that these Forsaken do is not really the relevant part of what I use them for.
Just as a for instance:
One of my R35 saves has someone giving these bonuses out at over 800% for the first and over 30% for the second. Like, that Forsaken is insanely good at making little low-cost Forsaken that can be summoned over and over again in the early part of loops, generating multiple future surrounds, as long as she performs the relevant T4 breaks. I don't have the experience to tell you whether this works out well at say, loop 25 or whatever, but it works pretty well in early loops.
The big thing that you should be focusing on with Forsaken is finding things you can't do with a basic commander and then optimizing the fuck out of them. Like, for example, a 4EE Forsaken can be gotten well before day 12 (they don't require upgrades for multiple captures or duration) and with the right bonuses and and attack types, you can have a Forsaken that breaks, say, everyone's T2 INN, giving you an early rush of EE and breaking you out of the cycle where the game doesn't start until day 12. A 2EE Forsaken can very possibly bring all 3 Chosen to you the first day you send her out, which if you feed the Breeding Pit, can be day 1. See if you can get Forsaken that break the rules in these sorts of ways.