I immediately liked your Alto Clef when I laid eyes on it, because it (obviously) suggests the B. So much, in fact, that it creates a challenge. (And your designs show that you see this.)
#11 was my least favorite at the start, because my eye's first reaction was that it was a crooked B. (And my less musically-literate clients will likely see it the same.) I've liked it more the more I've looked at it, but I do worry about it.
#12/
#13: I like the balance of these designs a lot -- very elegant, the font and the serifs of the clef, and the way the clef is counterweighted against the "music design." A little niggling thing of concern about design
#13 is the way the red line ALMOST (but not quite) lines up with the clef's middle guideline. Not sure if it needs to be changed; it just looks a tad messy. (Of the two options for the bottom guideline, I prefer the way 12's comes directly to the middle of the M of "music design.") As an alternate to #12 (and #11), I wonder how the clef would look not on the same line as the BLOOMBABER, but up above it.
#13 specifically: I think I need to show to some people and get reactions. Because I know it's a clef at the front, I worry that others will read it that way -- not as a B -- and see the word LOOMBABER.
These are great designs...hard for me to part right away, though, with the familiarity and beauty of the treble clef. Thanks so much for your work, and keep it up!