One of my favourite Star Alliance lounges is the Air New Zealand lounge in Sydney. The United Polaris lounges should probably also get a shout out
The most overrated Star Alliance lounge is the T3 SilverKris lounge in Singapore. Closely followed by the TK lounges in the new Istanbul Airport.

I dont have too much experience with SkyTeam lounges yet, though the CDG Air France Schengen lounge in 2F does a real good job. The 2K lounge is also pretty good food and drink wise, but a bit tired and too difficult to secure a power outlet. The Delta Skyclub in Haneda deserves a recommendation.