A1

From Brewer's Dictionary of Phrase and Fable by E. Cobham Brewer.

“A1 means first-rate—the very best. In Lloyd's Register of British and Foreign Shipping, the character of the ship's hull is designated by letters, and that of the anchors, cables, and stores by figures. A1 means hull first-rate, and also anchors, cables, and stores; A2, hull first-rate, but fittings second-rate. Vessels of an inferior character are classified under the letters AE, E, and I.