There is no one best restaurant. But those where we had tasting menu meals that were so spectacularly good that we easily remember them long afterward include:

USA:
Saison, San Francisco
Meadowood, Napa Valley
Saam at The Bazaar by Jose Andres, Los Angeles
Juniper & Ivy, San Diego
Alinea, Chicago
L20, Chicago
Le Bernardin, NYC

MEXICO:
Pujol, Mexico City
Biko, Mexico City
Quintonil, Mexico City

SOUTH AMERICA:
Central, Lima, Peru
Astrid y Gaston, Lima, Peru
La Cena del Oro at MAP Cafe, Cusco, Peru
Sucre, Buenos Aires, Argentina
1884, Mendoza, Argentina

EUROPE:
Noma, Copenhagen, Denmark
Geranium, Copenhagen, Denmark
The Ledbury, London, UK
Guy Savoy, Paris, France
L'Atelier de Joel Robuchon, Paris, France
Le Calandre, Rubano, Italy
Varvary, Moscow, Russia
Mikla, Istanbul

SOUTH AFRICA:
The Test Kitchen, Cape Town
The Tasting Room at Le Quartier Francais, Franschhoek
Camphors at Vergelegen, Stellenbosch

ASIA:
Amber, Hong Kong
Mr. & Mrs. Bund, Shanghai
Nahm, Bangkok

MOST OVERRATED "TOP" RESTAURANTS FOR US:
French Laundry, Napa Valley--very good, but not memorable & pompous
Lung King Heen, Hong Kong--very good, but not 3 star
Coi, San Francisco--very good, but not remarkable
Malabar, Lima--just good
Dinner by Heston Blumenthal, London--downright bad, 2nd biggest letdown
St. John, London--absolutely awful, worst fine dining letdown ever

STILL DYING TO TRY:
Benu, San Francisco, USA (in 2 weeks!)
Atelier Crenn, San Francisco, USA (in 2 weeks!)
Manresa, Los Gatos, USA
Chez Panisse, Berkeley, USA
Eleven Madison Park, NYC, USA
Next, Chicago, USA
Chef's Table at Brooklyn Fare, NYC, USA
El Cellar de Can Roca, Girona, Spain
Osteria Francescana, Modena, Italy
D.O.M., Sao Paolo, Brazil
Mugaritz, San Sebastian, Spain
All of Tokyo top restaurants!