France is probably regarded as the best source, if only because it has the largest reserves in Europe and the most varied. Quercus sessilis is generally regarded as the finest oak, as it has a tight grain and is rich in aromatic compounds. This is the species found in the Tronçais, Nevers, Allier and Vosges forests.
Les Blog » A French Oak Barrel Primer
French oak is commonly divided between two species, Quercus robur (which sports wide grain, or more space between the annual growth rings of a tree) and Quercus sessiliflora (a tighter-grained species). While a wider grain imparts more flavor to the liquid, tighter grained wood is generally preferred for wine, since barrels made from it are easier to make water-tight.