which jaffar should I use

It's really up to preference. If you keep Life and Death, you're choosing between a offensive line of either 49/38 or 45/41. He has a super boon in attack which can help taking out targets, but since Jaffar is primarily a mage killer with his refined Deathly Dagger, you may fail to secure kills without a follow-up. Its all down to preference, but I would personally go with speed as it doubles as both an offensive stat and a slight form of bulk.

As for builds you can refine his dagger with the effect if you hate mages, or go for the speed to boost him to 43. Add whatever positional you want and either keep Glimmer or swap it for Moonbow. Life and Death is already an amazing skill for him so I wouldn't recommend changing it.

Now you choose one of two options, to make him the ultimate chipper or a strong debuffer. If you want tons of AoE chip damage, go for Poison Strike with Savage Blow and Savage Blow sacred seal. For a more expensive but highly effective second set, you can give him Speed Smoke from a spare F!Takumi and then the Attack Smoke seal with whatever B skill you want.

Have fun building!

Both builds are good, he has HP to spare and both his defense stats are lousy. The two builds i have for mine since i like to spoil him are poison strike, double savage blow, and life or death for big field damage. you likely want attack boon on that for better odds of killing a squishy target lessing the chance of counter play. If you want to get gimmicky, he can run a double savage blow close counter vantage set, since deathly dagger will splash the enemy on their phase as well if he can land a hit. he can weaken an entire formation then protect himself and capitilize on the debuffs with vantage. That would benefit from a speed boon to lower the chance of getting blown up by a speedy ranged unit youd normally be keeping up with if you still had life or death. Universally, you likely want to replace glimmer with Luna or moonbow, since his attack stat is quite low.