Honestly, I had to figure this out by handling both at the hardware store-they sound the same, but there's a subtle feel difference.
A soft touch handle is usually a thin, smooth rubber or silicone coating over plastic or metal. It's soft to the touch, like the grip on a nice pen-comfortable, but not squishy. My soft touch knife's handle is sleek, so it fits in my pocket easily, and it doesn't collect dust or spackle crumbs as much.
A soft grip handle is thicker and more padded, almost like a foam or textured rubber. It's bulkier, but it's great if you're using the knife for hours. I tried my neighbor's soft grip one when scraping wallpaper-his hand didn't ache, but the handle felt too big for my small hands.
The blade and function are the same; it's just the handle's feel. If you do quick jobs (patching holes, scraping small areas), soft touch is lighter and easier to maneuver. If you're doing big projects (drywall finishing, whole-room wallpaper removal), soft grip might be more comfy for long stretches.
