Style X (see my list of cast ons here-- sub any cast on from the list for X) is MORE STRETCHY
Both of the above statements are true--(no matter which cast on you substitute for X!)
Well, many not quite true—maybe each is just a general statement.
What is true—Amost any cast on can be worked tight--(and will be less stretchy) and almost any cast on can be worked loose (and will be more stretchy).
Let me show you—the differences as I work are almost imperceptable. But the end results are VERY perceptable. (and this is something you can do your self at home.)--You can see a video of this demonstration here.
Take about a yard (more or less) of scrap yarn.
Fold in it in half, and place the yarn over a knitting needle. Twist the needle to make a loop.
Don't get (or do, if you want to!) get all anal about making sure the loop is EXACTLY at the half way point—just about even is good enough.
Then cast on stitches using a long tail cast on cast on--(sling shot or thumb style)
When you've run out of yarn, see how even (or uneven) the remaining yarn is.
With a long tail cast on, the thumb yarn makes a 'simple cast on loop' that is immediately “knit” with the index finger yarn. IN THEORY—both halves of the yarn should be usesd equally.
But—and it's a BIG BUT—if you over snug the thumb yarn, and make the 'simple cast on” part of the long tail tight—Well the cast on is going to be tight.
It takes some effort and practice (and there are other solutions) but you can learn to snug, but not tighten up the thumb yarn.
Look what the results.
In Sample 1—(the upper needle) the remnants lengths differer significantly.. the thumb yarn remnant is more than 2 times the length of the index finger remnant.
In Sample 2—(the lower needle)the remnants are almost the same length--(the thumb yarn is a bit (20% or so) longer than the index finger yarn remnant—so they are not exactly even, but close.
Stretch the stitches out on the needle—what do you see? Significantly more stretch in the second sample. When the thumb yarn isn't over tightened, the cast on is significantly stretchier.
If—instead of short lengths, these were actual cast ons for projects—one project would have a neat (certainly the loops aren't loose and messy!) edge with plenty of stretch, and the other project would have a much less stretchy edge.
Long tail cast on can be a stretchy cast on—or not!
I know that for me, I find it hard to get a loose, stretchy, and neat cast on edge with a cable cast on--It's not that cable cast on can't be all three things at once –It's ME.
The fault is not in the star's, or in the cast on, the fault lies with in ourselves (or myself!)
I find Long Tail to be a good cast on for me—But I recognize—there is no one cast on that is best--(or stretchiest, or prettiest or ...any other superlative).
I am sure, I could-- if I put my mind ot it—learn to do a neat, stretchy, cable cast on. It's with my power—but I haven't bothered. I like my version of the cable cast on—and I use a cable cast on when I want a firm, not too stretchy cast on! (for say a buttonhole)
When it comes to cast ons—there are so many factors that go into making a good cast on edge.. And some of those factors are totally within our control.