Most professional photographers work with full frame cameras. No surprise here, it is known to yield the best image quality. That said, the latest APS-C size sensors have improved drastically lately. The Sony A6000 and the Nikon D7200 and the D5300 are the proof that this sensor size can be excellent (for the most camera geeks of you, you will have noticed that these 3 have the same 24.3MP Sony sensor but Nikon has its own way of working with it).
This test here is showing how close it can be. The gap seems to get smaller and smaller lately, so is it worth upgrading your gear to have a full frame sensor knowing a full frame camera and all the lenses are significantly more expensive? There are many criteria to take into account.
Investing into a camera system can be very costly. The body itself is expensive but the lenses are the most expensive purchases. Fortunately, the lenses can last for decades if well maintained and treated. They also lose less value over time then the camera body. But even if we can change the camera body relatively more easily, the system we invest in determines the lenses you will buy.
Questions: Is it worth investing in a full frame sensor nowadays knowing the APS-C size (and even the micro 4/3rd sensors to a lower extent) have a great image quality, most of the time similar?What criteria are to take into account?