Central London Connexions became the first of the 47 partnerships in the country to be rated "excellent" in a glowing report by the Office for Standards in Education.
Ofsted also lavished praise on the Hertfordshire and Somerset services, rating the former very good and the latter as good. A fourth partnership, Derbyshire, was rated satisfactory.
The reports come at a time of concerns about the role of Connexions, and how it is to be funded.
The service has been ordered to save pound;25 million in VAT payments, which has led to the cancellation of several multi-million pound contracts with private providers.
Connexions managers are concerned about how partnerships will be affected by Children's Trusts, the new government initiative to integrate key services for children and young people.
A leading figure in one partnership said that instead of Connexions being directly funded as it is now, its money may in future be allocated by Children's Trusts.
He told FE Focus: "The problem is that Children's Trusts are based on local authority areas, whereas Connexions partnerships generally cover several local authorities.
"It would only take a couple of local authorities in a partnership area to decide they want to deliver guidance services independently of Connexions, and that partnership would become destabilised. There is no guarantee that trusts will commission Connexions."
But Central London Connexions is confident that it has a future after Children's Trusts are set up in 2006. Chief executive, Chris Heaume, said:
"This report makes us more optimistic that the trusts will be keen to preserve what has been developed by Connexions. A huge chunk of our budget already goes to direct delivery by local authorities."
Ofsted said central London has "developed effective strategies to ensure that young people receive swift and appropriate support".
"Leadership and management are excellent. Collaborative working with the statutory and voluntary sectors is outstanding, it said.
Ofsted also said the Hertfordshire partnership was "very successful" and highlighted "a significant fall in the number of young people not in education, employment or training in the area".
Somerset Connexions was described as having good leadership, effective in raising achievement and ensuring high quality support for young people.
Debate continues about whether the service should focus on young people "at risk" of dropping out of education and training, or if it should be a universal service for everyone aged 13 to 19.
This question was considered in a Department for Education and Skills "end-to-end" review of careers education and guidance, which will inform the Youth Green Paper, due to be published later this year.