SNTP is only useful as an option of last resort, e.g. you have no embedded RTC, and no storage to track drift. In all other cases a full NTP client is always preferable, since drift and corrections can be applied without causing jumps to the system clock (triggering software bugs and misfired events), and drift statistics can be recorded -- which is inevitably required in almost all circumstances where you're using even high end PC motherboards that still rely on a $.15 crystal time reference
