Acc and procs 
Your whole build should constitute to how you slot.
He will honor his words; he will definitely carry out his actions. What he promises he will fulfill. He does not care about his bodily self, putting his life and death aside to come forward for another's troubled besiegement. He does not boast about his ability, or shamelessly extol his own virtues. - Sima Qian.
*jumps into Mids*
After a bit of playing about, I'd say Efficacy Adaptor: Endmod/Endurance, Endmod/Acc (1.13% Hp boost), Cleaving Blow Acc/Dam, Scirroco's Dervish Dam/End, Damage Proc (10% regen boost), Muiti Strike Dam/End.
If all 50, That's 53% acc, 78% dam, 78% endred, 53% endmod and a chance for extra Lethal damage
I am the Blaster, I have filled the role of Tank, Controller and Defender
Sometimes all at once.
Union EU player! Pip pip, tally ho, top hats and tea etc etc
A little bored of generic IOs on my level 50 Brute after several months. Would like to get him slotted up with some more fancy stuff.
I'm a little stumped as to what would be the best possible combination of IOs/SHOs to get the most out of Lightning Field, though. I'd love to be able to get as much as possible out of four attributes here: Accuracy, Damage, Endurance Reduction and Endurance Modification. Frankenslotting, obviously?
Six slots. Suggestions? Browsing the black market has so far managed to confuse me. I don't do much IO-ing or HO-ing normally so anything more complex than frankenslotting the res shields for 91% res and endredux (and some rech) with only 4 slots makes me grumble.