So this is way over my head and I’m sure you can get into the weeds quite quickly with this subject.
Using the Mikrotik LtAP with ACGPSA GPPS antenna. (ROS 6.47)
What is a more accurate method of setting the clock, GPS or SNTP? From a quick google, I realise this isn’t a Stratum 1 device. So would it even matter?
Also how often does the clock poll the GPS? Is it possible to see this in RouterOS?
TIA
I expect GPS to win, even without PPS support. NMEA output gets sent every second (at least, that’s what I have seen with other GPS timing receivers) and assuming the router clock gets updated every second as well, that gives a more accurate clock than SNTP, which only updates it every 15 minutes.
Not really. NMEA output is approximately every second, but exact timing is not defined … so if one only relies on NMEA telegrams, precission is ± 0.5 seconds (or more likely something between 0 and +1 second). With PPS one gets exact timing (within micro or even nano seconds). The thing is: NMEA telegram contains time valid at the time of telegram preparation and is truncated to one second precision … depending on length of NMEA telegram and bitrate of serial connection it might take considerable time between that moment and moment when receiver sees the information and (even worse) the delay is not deterministic.
With SNTP precission is usually within tens of milliseconds, largely depending on network conditions (delay jitter, delay un-simmetry, …) …
You’re absolutely right. It’s been too long since I played with NTP and GPS timing receivers 
To your consolation: I’ve played with GPS and NTP a few days ago (installed a Meinberg LanTime M200 NTP server) so I refreshed my knowledge 
BTW, the said unit (running pretty stock linux and NTP server internally) synchronises to GPS receiver every 8 seconds:
ntp-s1 ~# ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
oGENERIC(0) .GPS. 0 l 3 8 377 0.000 -0.002 0.004
I would say it does not matter. GPS will give more exact time then NTP, but both are good enough to give you correct time. When going up the NTP chain three you will see that they uses GPS as well to get their time synced.
I disagree and I already wrote why that’s not the case without proper NTP/GPS support inside device in question. Details matter if one wants to get accuracy better than 1 second and for that, setting up SNTP is way better than off-the-shelf GPS receiver not meant for time keeping duties (i.e. lacking PPS output).
High-level speaking: yes, GPS is very good and very affordable source of precise time globally and yes, most stratum-1 NTP servers globally use GPS receivers as source of time.