It's really situation dependent. And by that I mean, where is your opponent approaching you from or if they are in-front of/behind you. Up-Tilt and B-Air are Kirby's 2 best options when it comes to stopping an opponent when they are hitting your shield as while your back is turned to them. Both come out pretty fast and have decent priority. I tend to use Up-Tilt alot against Sheik and Mario because of this.
D-Tilt/Jab/Grab, all 3 are a great of the opponent is in-front of you. As you know, Jab has a great chance of tripping and this works out in our favor well because of our grab follow-ups. While Jab can be SDI'd out of, it's still good for building up percent. And grab, well that goes without saying, Lol.