I will give my opinion based on Nikon full-frame versus Nikon APS-C sensor cameras. What I like about full-frame is that you have better iso performance and can get cameras with more megapixels. The viewfinders are also larger. The most significant advantage of full-frame is you have a bigger selection of lenses, and Nikon builds better quality full-frame lenses. Unfortunately, Nikon tends to build mostly consumer-oriented lens for APS-C sensor cameras. This makes sense to keep the cost down since APS-C sensor cameras are marketed as a lower-cost option.
Take, for instance, if I want a standard focal length prime lens for a full-frame camera. Here is what I can get:
In an APS-C sensor camera, I can get the following:
As you see, I can get five lenses for my full-frame camera, and I am limited to just two lenses for a Nikon APS-C camera. Also, note that the 35mm f/2D can be used on a full-frame camera and was originally intended to be a slightly wide-angle lens on full-frame cameras.
All the full-frame lenses have a focusing scale. The AF-S DX 35mm f/1.8G does not have a focusing scale, and this was left off to save money. I like a focusing scale and use it if I am doing night photography. You also cannot get as fast of lenses for your APS-C sensor camera.
If you want the best lens selection, you need to have a full-frame camera. Nikon has intentionally made lenses not as good for their APS-C sensor cameras.
The most significant disadvantage to full-frame lenses is that they will typically cost more. The prime lenses generally are the same price, but if you get into zoom lenses, you will be paying more. I find you pay about 40 percent more.
Now let’s get into the advantage of an APS-C sensor camera. In real life photography, you will probably not notice a difference. The majority of APS-C sensor cameras come with 24-megapixels, which can make a print up to 24×36. The ISO performance is typically one to two stops less than a full-frame, which is not much. Most people don’t need a 45-megapixel camera, and APS-C sensor cameras have excellent ISO performance. You also have to ask yourself, are you happy with a f/1.8 lens, or do you want the ability to use a f/1.4.
Ultimately, I think an APS-C sensor camera gives the best bang for the buck. If you are not concerned about cost as much, buy a full-frame camera, which will be better.