I just tried two tiny swatches of stockinette st to see what happens... It looks like there is always a small gap/hole between the left side of work and the left CO sts. [This can be remedied: see below.] Anyway, I think you can do the backward loop CO at the beginning of each row and not have to switch the direction of your loop to forward loop CO. If you're picky like me and want the ridges of your loop CO to match your initial CO, read on...
When doing the loop CO, do the backward loop CO at the beg of each row or do forward loop CO at the beg of each row, but don't do both. The backward loop CO matches the slant of the ridges of your initial CO if it was in long tail or backward loop. The forward loop CO seems to match the slant of the ridges of the knitted CO and cabled CO.
Also, I like to use my right index finger to wrap the yarn since I normally hold the yarn in my right hand anyway. Holding the working yarn with my 3rd, 4th, and 5th fingers, I wrap my finger around the yarn "down and away" from me going in front of the yarn to do backward loop (this is opposite what you'd do with your left index finger). This means I have to catch the loop behind my index finger rather than in front (Just curl your index finger toward you). For forward loop CO, I wrap the right index finger around the yarn "down and toward" me, going behind the yarn. This comes from The Knitting Answer Book by Margaret Radcliffe.
Actually, I use the Knit/Purl CO most often for mid-project COs. For the Knit CO and Purl CO, I believe that it does matter which one you use on the knitside and purlside. I use the Knit CO at the beginning of a knit row and the Purl CO at the beginning of a purl row. I've read that the Knit CO looks the same no matter what side it is worked. This may be true, but I still feel better if I do a Purl CO at the beginning of a purl row! :twisted: Crazy me!
To tighten up the gap/hole between CO sts and the other sts: Pick up an extra stitch before casting on and mark it. When you come back to it, do a K2tog/P2tog (depending on which side you're on) with the picked up st and the first CO st. I got this idea from Grumperina in her Picovoli pattern at MagKnits.