Definately the C2 Duo...however availability will certainly be an issue for awhile.
As Anand pointed out in the article from Computex,
"There is a lot of concern about the availability of Conroe, as Intel has only committed to around 25% of its mainstream and high end desktop processor shipments being Conroe by the end of this year. After Dell and HP buy up all the Conroes they will want for their systems, there simply may not be any left for the end user to buy in the channel market. Alternatively, there may end up being some supply in the channel market but at significant markups due to a shortage"