I don't have any forms of reference on me, but i believe that only moridin could challenge him among the forsaken right now. Rand has achieved a greater understanding about life, but so has moridin, it seems to me to be the balance. Rand's achievements are based on love and the desire to live again and again in the cycle of the wheel(what he discovered on his grave). Moridin seems to have achieved a piece of mind too, just completely opposite, i remember a few scenes where he seems to understand more than the other forsaken, he understands that when the dark lord wins there will be no more life, period, he seems happy about this. While all the forsaken are still competing and thinking about what to do when the great lord wins to get in his favor, Moridin is not, he knows that when the dark lord wins all is over, this seems to make him happy and completely contempt. It's almost the complete opposite, rand achieved greatness through the thought of life Moridin through the thought of death. This is theory of course because we've never seen Moridin demonstrate great amount of power, but it seems to make sense to me at least.

This of course assumes rands new powers are based on what happened at his grave.