This stitch is probably the most commonly used of the variations, though it is probably not thought of as a shell stitch. This is basically the backbone of the shell stitch: any stitch that wouldn't be crocheted into on the next row is replaced with a chain. It's a lacy look, but also well defined. You don't have to work a stitch in a space at any time. The result is vertical stripes and diagonal lines. It creates hexagons, which could be useful. Imagine a swatch of simple shell stitch, with this variation used to put a hexagon in. I'd have to diagram it to make sure I get it right, but it'd be neat looking.
So here's the pattern:
Chain a multiple of 6 + 5
Row 1: sc in 2nd ch from hook, (ch 2, sk 2, dc, ch 2, sk 2, sc) across, dc in last ch
Row 2: ch 1, turn, sc, (ch 2, dc in sc, ch 2, sc in dc) across, dc in last sc