My favorite of the bunch shifts between defender & yellow.
I am happy that I switched to an bolder pencil for the black ranger. That being said, I had to redo his mouth many times before I let it just be, the first time I drew it made it look horribly crooked. Invest in good erasers.
The green ranger has a nice shinny look to him that pops out.
I would use a darker bold for yellow looking at it now. The charcoal was really a crutch, but they were a mess to erase or lighten.