D70s to D90 or D300?

Just curious if anyone out there has made a switch from the D70s to either the D90 or the D300 and which would you recommend as the smartest progression! I am an amateur phorographer who wants to grow more in my understanding of light and PP.

My only complaint in the D70s is the concentration of low light provided in the images to avoid blown highlights, which minimizes the burst of true color that so many users of the D50 loved!

Thanks for the help.

Ron
D70s
18-200 VR