Just finished a swatch with the 3 methods: slip instead of k into back loop; standard kf&b, and twist kb&f (Knitting Nuances new take). I will post photo when it is dried - currently on blocking board.
Initial observations: slipping back loop leaves a hole, which can be used for decorative effect. However, if the knitted fabric is not going to be under any tension at all, the hole wouldn't be visible as the previous stitch and the k into front loop snug up together. Just a little sideways tension on fabric reveals the hole.
Comparing the other 2, the kb&f definitely has a smaller visible bar then standard kf&b. Without doubt results would be different with different yarns. I used an 8 ply crepe. With a less defined yarn I think the kb&f bar would be even less visible and disappear more into the fabric.