#2 is still looking the strongest - kind of abstract and it's cool!
The balance of orange and green, and the purple accents are working really well together. Maybe just change the lightbulb to a drop icon, or something more abstract.
#18 looks strongest, except the purple curved into the orange in the middle isn't working somehow. The purple looks good on the edge of the orange center - but the way it cuts into it near the top breaks the flow.