[djedr]

I suppose a bit of both.

I was more directly inspired by Lisps, but I do prefer the original M-expressions and the syntactic choices that REBOL and Red make.

I think placing the operator before the opening bracket better emphasizes its special significance and can reduce nesting for constructs like `f[x][y]` (vs. `((f x) y)` in Lisps). Square brackets somehow seem more aesthetically pleasing to me. And there is a practical reason to prefer them, especially if your syntax uses only one kind of brackets -- square brackets are the easiest to type on an average keyboard.

So REBOL-like syntax is nicer. As were M-expressions. They probably didn't catch on, because they were not minimal enough, compared to S-expressions. And maybe because S-expressions were fully implemented first.