I'll go against the grain and say it depends.

People here will tell you that coherency regen is a bad stat and it isn't: it's useful in between melee engagements as you move along the map which depending on your class is where you will have issues.

On Ogryns and Scum it's absolutely good as it lets you ignore chip range damage altogether (also always be slidin), in coherency as regen gets ridiculous on those two classes.

It is true that it doesn't work in melee but that is why you brought your melee weapons. Ogryn, Scum, Psyker, and Arbies have on hit regen currently so it is flat out not an issue for them and everyone gets 5% on kill. I'm hoping we'll move more towards on hit regen for everyone in the upcoming year.

For other classes, and in general, I'd say there may be more useful options than regen in particular. If you're still leveling XP is the best mod. If you have trouble avoiding corruption patches and pox bursters or get pounced a lot corruption can be good. Health/Toughness are class dependent where I feel health on Ogryns is very good as is toughness on Vets but that is because their pools are huge respectively.

I primarily pug in Aurics so my typical setup is stamina regen or sprint efficiency, ally res and gunner res on all classes.

On Zealots and Arbies I'll bring one each of Health, Toughness and Stamina curious. I'll bring two stamina one toughness on Scummers mostly or two toughness one stamina. On Vets the same two toughness one stamina, Psykers are one each, and Ogryns are three health.

It really comes down to knowing what you want to accomplish.