the fill light is very practical!
considering the site conditions and shooting needs, then I suggest using the hot shoe flash.
let's talk about the fill light first. If it is portable, the always-on fill light is inconvenient to carry, which requires a certain period of battery life, and the battery is even bigger. Then, as far as the brightness is concerned, the light emitted by the fill light lamp is generally weak, and the light added to the photographed object is poor beyond five meters. It is still possible to turn the iso slightly higher for shooting within five meters. Look at the advantages of the fill light, which is always on, and it will be easier to grasp the picture (the natural combination of light and something); The fill light can have the function of double color temperature adjustment, which will have a certain impact on the tone atmosphere of the camera directly. However, taking photos is not a video. If you need to do post-production, it should be unnecessary. The light emitted by the fill lamp is relatively soft and full, which is natural. If you use a flash lamp, you need some experience to grasp the light problem of a piece.
look at the flash, which is relatively small and easy to carry. The instantaneous light output is seconds, seconds and seconds, and shooting can make the scene light up under any circumstances. Disadvantages,,, can only be said that you are inexperienced and can't arrange the light. Don't point the flash directly at the subject when shooting, or the light will be hard, bright and dark, and unnatural. Generally, flash is used in shooting, that is, flashing at the side or top wall, and then illuminating the subject through the reflected light from the wall. It is recommended to play with manual flash, high-speed synchronization and TTL should be considered as two functions that I personally think are relatively tasteless. The light of the flash is pure white light, so it is impossible to set the color temperature, but the photo is taken late and there is no pressure.
What kind of camera is the subject? Canon Half Frame and Nikon all have their own flash. You can use the camera's own experience first. If it is a full-frame machine, ISO need not be limited to that stage. I shoot ISO indoors directly at 25, as long as I do well in the later stage, I don't have to worry too much in the early stage.