>>4215338It depends on what kind of stuff OP is planning to shoot. Films and documentaries, or corporate, social media etc. content? Is he planning to work solo/with a small crew or will he be working a with a bigger crew with more specialized roles?
FX3 lacks some important features that would make it ideal for run and gun, for example it has no internal ND. But it is compact and you can shoot it with straight out of the box, especially with a Sony lens and make it work. It has better controls and buttons for a solo shooter. It probably requires some rigging for certain kind of filming, but both the Blackmagic and RED need more rigging and cages to make them work. FX3 has Sony's great autofocus. Not all kinds of video production demand or use autofocus, but it is once again used by many people, especially people who do smaller run and gun stuff like weddings, social media content, smaller scale commercials etc.
FX3 has IBIS which again is good for certain kind of smaller run and gun productions. Straight out of the box it is gimped when it comes to audio, but so are the Blackmagic and RED cameras.
Sony's hardware is more reliable than Blackmagic's and their quality control is better. RED cameras are to this day quite finicky for their price range. Still occasional overheating problems, they crash more etc. I work as a camera assistant and they always cause more headaches than Arri.
Benefit of Blackmagic is obviously the amazing RAW, same with RED. But not everyone needs RAW and that workflow. Both RED and Blackmagic do ProRes which is really great and convenient. With both of these cameras you need to rig them considerably more to make them work. Especially with RED it can become really expensive for a solo shooter. Lot of the stuff to make it work is still either proprietary or just other wise more expensive.