I like heals and debuff, myself.
I slot mine for mez/debuff - the heal is still useful but if I need a heal I don't want to be relying on the pet's whim as to whether it fires it. Fluffy spams immobs in any event so probably not a huge benifit from slotting that but its hold stacking with PG can be very useful.
But the best slotting will depend on your playstyle and also the rest of your build.
Mind of Gaia lvl 50 Defiant's first Mind/Storm 'troller.
Deadly Doc 50 Dark/Dark Corr
and lots more on Pinnacle,Union and Defiant
I'd say whatever suits your toon and playstyle. Servant has a nice tohit debuff even without slotting, so I've left that alone, and have gone to heal and hold instead.
My main toons on Union:
Majer; Dark/Dark Corruptor
Caitlin Calathea; Plant/Thorns Dominator
Davallia Fejeensis; Empathy/Archery Defender
My arc:
ID 98789, What once was, will be again.
Thks all.
Personally slotted mine heavily for recharge and tohit debuff as I herd a lot on my fire/dark so there's a lot of resummoning involved.
SingStar:
"Extremists LOVE to fish to get us annoyed so we break the forum rules."
CRACK68:
"The origin of life wasn't planned either, should all life be declared a bug and wiped out?"
Lionsbane:
"You know me.Ever the realist"
HOs can be useful for Dark Servant - I plan to use them on my Dark/Sonic Defender and my Rad/Dark Corruptor at 50, and to re-slot my MM's Dark Servant with them (he currently uses Hold and ToHitDebuff IO sets in it to softcap -ToHit and Rchg, and get Hold Duration and Accuracy quite high). Mix Lysosomes (Acc, DefDebuff, ToHitDebuff), Golgis (Heal, End), Endoplasms (Acc, Mez) or maybe Peroxisomes (Dmg, Mez) to taste.
The Endoplasms/Peroxisomes can be particularly nice as they will affect both Fluffy's Petrifying Gaze and Tenebrous Tentacles. Though personally I lean towards Lysosomes as it buffs the ToHitDebuff on their Chill of the Night aura, their Darkest Night and even their Twilight Grasp - on top of your own debuffs that's a lot of -ToHit on an AV. If you solo more then you may prefer focusing on +mez or +heal as it will probably help you more often.
Whats the best way to slot this thing?
heals
hold debuff?