That is a good question and It seems different from one person to another. I have personally started following the good advice from kloner and got a 7 in. monitor. It works great and I am very happy with it. Framing videos is now a charm. My monitor is installed on a fully extended tripod and basically sits beside the multirotor when I look up. This way, I can quickly switch view from LOS to monitor which allows me to precisely control my views.
Having said that, I had to try the goggles.... And In did. Got a pair of Fatshark SD Base and plugged it in the DJI 5.8 mHz receiver. Pretty wild.... It is an entirely new dimension, difficult to explain without trying it out for yourself. There is a poweful initial WOW effect and it is, as frequently reported, quite disorientating (if this word exists...). I believe that the monitor is the safe bet and the goggles' appreciation will vary from one person to another. Even with a few thousand hours of full size flying as a former professional pilot (Air Force), I felt a bit funny after the first few minutes but things got better until I took them off for landing! Just like walking out of a theater and looking at the sky. I could hear my multi rotor but was totally blinded by the light. Not a good feeling! Also, I must mention that the occasional fogging of the goggles is unpleasant but goes away rapidly, as you pull the goggles away from your face for a few seconds. To some extend, I think it is related to the pilot heartbeat...
In summary, a monitor is really great and is relatively easy to get used to. On the other hand, goggles have a lot of potential but do not look for instant gratification, they need to be tamed first.
Happy flying!