I've always felt that Spectre (Hal Jordan) had the potential to be the most powerfull version of the Spectre.
He pretty much 'expelled' the wrath and discovered the Logos, aswell as potentially untapped energy being discovered as he evolved. But his human vision pretty much limited his power and never became what he could have.
Originally posted by Galan007
On a sidenote, I do feel as though Criss has the greatest potential - just hasn't realized it yet.
From the interviews up until now on Final Crisis: Revelations, it seems that Spectre's potential will be heavily focused on.