ranking the CC chess sites

hi all i'm looking to improve my game and my thoughts have always been
that you wont get better unless you play better players than
yourself.  i have been trying out several of the CC chess sites and
was wondering how one would rank the following sites as to the
strength of the competition.  i have my thoughts as to which one has
the stronger players but would like the imput of others.  the sites
i've tried out are as follows:

gameknot

redhotpawn

schemingmind

queenalice

chesshere

thanks again for all you imput