Edit : To answer OP (I digressed) : Check in your species panel what the slave policy is for the races on this planet and change it for what you would like. If you want the specialist jobs to be filled free some of these slaves or resettle non slave pop on the planet. Remember that servant can work any worker job, until there is no more, then will work as a servant instead of being unemployed.
If you had to compare them (to chattel slavery) :
- Chattel Slavery : +10% Pop job.
- Domestic Servant : +10 happiness, 1/3 of housing used if working as servant. + 4 amenities
- Battle Thralls : +10 happiness, +20% soldier
- Livestock : -20 happiness, open only to xenophobes, 1/3 housing needs, + 4 food
So :
- Chattel Slavery are the best workers. You need 1 per worker slot.
- Domestic for entertainer only, and for reaching stability cap (best secondary ressources boost) or unlocking buildings slots. They shouldn't do anything else. You need 1 per Entertainer Job + X until Stability cap or Amenities cap, what ever comes first.
- Battle Thralls for Soldiers only and nothing else. You need 1 per Soldier Job
- Livestock is kinda tricky. Best boost to food clearly (4 chattel farmers : 24 food -4 job -3 housing, 6 livestock : 24 food -0 job -1.5 housing) but it will lower your stability, thus lower your secondary ressource output. They are the best early game, and work as long as you can cap stability consistently mid/late game. You need everything else to be livestock until stab below 100%. Purge the rest.
In order :
- Entertainer : 1 Servant for each
- Soldiers first : 1 Thrall for each
- Other worker jobs : 1 Chattel for each
- Stability/Amenities Cap : Rest on servants
- Stability Over-cap : Rest on livestock
Population control based on needs