MOA or MRAD?
Well here's the simple fact, neither. These are simply two ways of measuring the same thing.
Two ways to do the same thing.
When I was in the US, I’d drive past the ‘gas station’ and see the price per gallon. This meant nothing to me, as living in Australia all my life, I haven’t a clue the amount of fuel that makes up a gallon. I’m sure the Americans feel the same when they come over here. Its still fuel, the tank size in the same car is still the same, but we have a different language around the measurement system we use.
And so its the same with MOA and MRAD (Mil/Milliradians). These are two angular measurements. So if you see a rail that has a ’20 MOA’ cant, it is also has a ‘5.8MRAD' rail. If you need to move your bullet 1 MRAD to the left at 1000m, you could dial it 3.6MOA if that is what your scope is using.
One thing that is often said is that one is Metric, one is Imperial. This is not strictly true. If MOA was imperial 1 MOA would be 1” at 100yards, not 1.047… However, often people familiar with either system will gravitate towards the one the closest resembles the language they are most used to.
Which one to choose?
If you lived in the US, it would certainly make life easier if you understood measuring fuel in gallons. Communication with other drivers and station attendants would probably be simpler and easier. If you are in Australia, understanding and using litres would make sense and reduce confusion. So it is really about the context and environment you expect to be driving in. Or shooting in as the case may be.
Rather than geographical lines, MOA and MRAD seem to be split by shooting disciplines. F-class, Benchrest and general hunters have used the MOA system for years. Especially in the competition shooting, wind calls and drop data are commonly given in MOA. Disciplines such as PRS, PRC, Long Range hunting and others have trended more towards the MRAD system. There are reasons for these, but they are for another discussion how they came about.
The important thing is knowing the context and the people you will be shooting with. Having turrets/adjustments/reticles that match the common language of the sport will make your life much easier. Don’t worry. At the end of the day, the ability to hit targets has no direct connection to the measurement system you are using. As long as the fuel is good, your car still drives.