Perhaps PPLNS on mineco.in has the highest expected return without the extreme variance of solo mining.
Oh, why that particular pool? Something the other PPLNS pools don't have?Personally I mine PPLNS at simplecoin.us (I lose block reward transaction fees but gain more in reduced stales).
Their site seems to be down at the moment, so I can't compare stats, but ours has phenominally low stales too, and transaction fees are rewarded to miners 