Ibot,
I'll try and give you feedback on each (or in groups):
You're use of the dollar sign ($) works better in #20-23 than in #13-16 which seems kind of literal (beaker full of liquid money) which seems showy.
All of the labs seem gray and not black to me, though the black eyes/nose helps a little in #20-23.
The lab used in #22 and 23 isn't cute/playful at all. The lab in #20-21 are probably closest to what we're looking for, but some of the other submissions are a little closer.
Thanks for all your submissions,
John