Because ping is the speed at which information is sent and received, factoring in packet loss, lower numbers are always better. Ping varies based on many factors, so while an ideal ping might be 5 milliseconds, an acceptable ping could be 15, 20 or could even spike into the hundreds.
High ping can be annoying for average Internet use, because it causes slow response from websites and is associated with less-than-optimal connection speeds. High ping can be particularly troublesome in competitive gaming. Because ping is the amount of time required for a signal to be sent from a computer to a server and back, reducing that speed slows down both action and player reaction.