Assuming that the Jigglypuff is DIing properly, shoryuken starts killing from the ground at 54 on Dreamland (the stage with the highest ceiling) and at 36 on Yoshi's Story (the stage with the lowest ceiling). So shoryuken is the best option at and above those percents on those stages and all other stages are somewhere in between. Misfire kills at lower percents, but when it kills is dependent on stage position and how many times you've stored it, so it's not that reliable.
I'm think that the optimal punish at lower percents involves the dair meteor hitbox. Meteor dair into shoryuken kills like 5-10 percent before grounded shoryuken and does like 37 damage. The problem with it is that it's pretty hard if they DI, and not guaranteed with good DI and good SDI. It's also pretty difficult to get the meteor hit of dair in the first place. At 10 percent and below, Jigglypuff doesn't move from the dair, so after the dair meteor combo using up tilt or up smash, or maybe do turnaround grounded shoryuken.
I don't recommend jab shoryuken, since most good Jigglypuff players will be ready to DI/SDI the jab if they know you punish rest that way.