I've tried Slush, Simplecoin and nmcbit.com, and I'm currently using nmcbit. Slush may be the best, but it's hard to know for sure because we haven't actually got any Namecoins from him yet. Simplecoin finds suspiciously few NMC blocks. The hash rate of nmcbit.com is a bit low, but at least it finds the expected number of coins, and pays them out quickly.
Agreed. Simplecoin is reporting
very few blocks for the hash rate it receives but this is most likely due to problems with the SQL stats replication server. It would be wise to wait for simplecoin.us to start reporting normal luck before joining that pool, putting pressure on the operator to get the stats sorted as soon as possible.
I didn't know people hadn't got namecoins from slush yet but I would be startled to learn that he had anything other than honourable intentions. Consider masterpool.eu, nmcbit.com, eligius.st and keep you eyes open for news from other merged mining pools. Avoid raw proportional (unless your hopping), spread your resources (reducing variance) and configure backup pools; the next two days are important (low Namecoin difficulty).
