In reply to Hiking_Dad:
We parked at Cad West, there is a big layby for 20ish cars and about a 15min walk up the hill.
https://machloop.co.uk/ This has plenty of good info on access and locations.
In terms of spotting aircraft, it is pretty random. They only use the loop Mon-Fri and the MOD low flying schedule has no resemblance to what actually happens. It is very much a case of take some snacks, a flask and go and sit and wait.
Clear weather will increase your chances, as will bad weather in the Lakes or Scotland.
You can also use 360Radar or https://globe.adsbexchange.com/ to track what is about. Just hit the military filter to get rid of all the commercial stuff.
I think the Hawks and Texans from RAF Valley are probably the most common. The F15s and F35s will come from Norfolk, so you can keep an eye on that area with the tracker.
Hope that helps and you get to visit