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 
Looks very good. I only mentioned mineco.in because it was the only pool I knew of (before your post) that did offered PPLNS, 0% fee, and transaction fee rewards (I know they are small right now but this is a big plus in my book). For me, the grace period for supplying shares for a recently expired round is technically a minus. Other than that, the list of features is impressive though I would expect to see some mention that there is no fee on BTC withdrawals. At 25 Gh/s the variance is fairly high but I'm sure it's much better than solo mining for most people.
Given I don't have anything like a complete list of mining pools, I'll rephrase to say that right now the best bet seems to be to find a 0% fee pool using PPLNS and which includes the transaction fee reward. Avoid PPS unless you've calculated the expected return vs. solo carefully and are happy with the reduction. Definitely avoid proportional unless you intend to pool hop.