Which word best describes a person who tends to lounge or act lazily?

The word "loll" is the best choice to describe a person who tends to lounge or act lazily because it specifically conveys the idea of lying or sitting in a relaxed, lazy manner. It suggests a carefree attitude towards activity and a tendency to indulge in leisure without much effort.

In contrast, "vivacious" describes someone who is lively, animated, and full of energy, which is opposite to laziness. "Loquacious" refers to someone who is very talkative and outgoing, which doesn't directly relate to a lazy disposition. "Phlegmatic" characterizes a person as calm and composed but can also imply a lack of energy or enthusiasm, though it doesn’t specifically suggest lounging or laziness as clearly as "loll" does. Therefore, "loll" stands out as the most accurate descriptor for someone who prefers to lounge around idly.