Sodium C14-C16 Olefin Sulfonate is supposed to be more gentle than C12-C14, and I don't doubt it for a second, but I haven't actually compared the two myself or anything.
I do know both are more harsh than SLES, which actually isn't so bad as people make it out to be. I personally prefer it as my scalp had issues with a lot of milder stuff. Yes, issues, very bad ones.
Compared to SLS, it should be similar or slightly milder. Of course, formulation is key...
If you're going to try either I'd go for the C14-C16.