any opinions on how good soft catch traps are compared to the old jaw style?

I've never used any but the word is that the jaws are very slick and you get a lot of pull outs with them. IMO, a proper sized trap with an offset jaw is the most humane way to go.

Have used the #3's on coyotes with decent results, too pricy for my blood though.

Ive used the soft catch with good success. Ive caught coons, possums,cats,a dog, and a big red fox and nothing pulled out. The soft part is rubber so it is not easy to pull out, and yes they can be expensive...about 20$ a piece. Good luck, if you need any ideas on how to set them private message me.

Do jaw style traps kill or just hold ?

they just hold and do no damage to animal if set properly. Most DNR's use foothold traps to catch animals for relocation and restocking efforts.