Depends on whether you're running him under Palp lead or his own lead.
Palp lead go with crit chance/crit damage and speed, and potency primary on the plus mod. Use a health primary on the circle mod because he'll be getting a lot of health back.
If he's the lead you're gonna need potency and speed and then probably some crit chance as other said. You need the potency for the DoTs to stick, but the TMR can't be resisted. Speed is always key so you can get more turns and more TMR and more DoTs in. You'll probably want protection as the primary for the circle mod if he's the leader because he won't be doing as much healing as he would under a Palp lead.
I've gone all out on Critical Chance to make that culling blade count (I've thought about going down a similar route for Boba, but if his CC gets high enough as you gear him then I'll favour CD). I run him under a Palp lead for GW so with a potency cross, he lands his debuffs at a decent rate. With a 5-dot triangle with a CC primary, I got his CC up to 58%. He consistently does over 30k damage to characters with four debuffs and with some patience, it could do more.
Replies
Crit dmg triangle, and speed arrow
Secondaries:
Potency>speed>crit chance
I would say in that order but if you have a mod that carries all, even better!
Palp lead go with crit chance/crit damage and speed, and potency primary on the plus mod. Use a health primary on the circle mod because he'll be getting a lot of health back.
If he's the lead you're gonna need potency and speed and then probably some crit chance as other said. You need the potency for the DoTs to stick, but the TMR can't be resisted. Speed is always key so you can get more turns and more TMR and more DoTs in. You'll probably want protection as the primary for the circle mod if he's the leader because he won't be doing as much healing as he would under a Palp lead.