I like the #3 by sadface.

I found that the logos are tend to be fairly simple. Decorative things can be added later when necessary.
For example, here is the logo of Monero ("M" in circle + plain font) and Qora (which denotes the same "Q").

I think that the basic shape matters the most and my summary of top candidates is as follows:

#3 (circle + horn)
#10 (circle + ball)
#11 (loupe + 10-point-star)
#12 (circle + tail)
#13 (circle + backslash)
#18 (#11 + #13)

Actually, I was surprised such a cool logo has not been owned by some entity yet (the #3).
It looks like sending a signal that pretty matches with a quasar!