besting

at one's best, in one's best

这两者意思容易混淆。前者是“处于佳境”,后者是“穿上盛装”。例如:
I'm at my best in the early morning.我早晨精神状态最佳。
Children have been all in their best during Christmas.孩子们在圣诞节都穿上了最漂亮的衣服。