I will describe several pressure regulators and comment.
Standard, this is a cylinder, about 3/4" (Garden hose fitting) Size male and female fittings one on each end, Restricts the flow like you'd not believe.
HI-Flow, or capacity, LIke above but with bright plastic grip on female end or wings (Camco) on body.. Same comment.
Sur-Flo.. Slightly better, this is the standard "Inlet regulator" see comment below on placement.
Watts, Valterra or Zurin "Whole house" regulator, mine is currently a Zurin, replaced a damaged Watts. Both it and the watts are 3/4 inch. Th Watts is something like 8 years old.
Supply side around 100 PSI,, Pressure setting 50 psi. Load = outside shower (What I usually call dog shower) in wet bay.
Sur flo,, Static 50 psi, loaded 10
Watts (old, damaged an in need of re-build kit) Static 50, loaded 20
ZURIN (Brand new still just out of the box first day of use)
Static 50, loaded 50, no change.
I am not claming the ZURIN is better than the watts, Watts worked better when it was new and just out of the box.. I'd recommend either
Valterra I've not tested..
Why 3/4 inch? Well, easier to find 3/4 to Garden hose adapters for one thing..
Pressure in this park has been measured at upwards of 120PSI, from time to time, at that pressure the ends often come off hoses.. SO the hose from the spigot to the ZURIN is a strain relief armored hose that should be able to take it.. The long white one,, not so well but then it does not have to since the ZURIN is in the way of the excess pressure.
Very happy with it, sixty bucks (rounded) at local plumbing supply. Includes fittings.
Home is where I park it!