What's the best way to synchronize times to millisecond accuracy AND precision between machines?

From what I understand, the crystals on PCs are notorious for clock skew. If clocks are always skewing, what is the best way to synchronize clocks between machines, with millisecond accuracy and precision? From what I've found, NTP and PTP are possible solutions, but I was wondering if anyone else has had any experiences with PTP (IEEE1588).