I second what dark_lord69 said. It's all relative to how close you sit to it.
Expanding a bit more: 2 to 3 feet from screen and 24" or 27" are ideal, 6 to 8 feet and then 55" to 65" tv's are usually ideal.
Also pay attention to the contrast ratios, nit, refresh rate. For the most part-higher is better. For a monitor I recommend 100-144hz depending on what your rig can push. 60hz is fine but higher can be really nice for FPS or racing. I've also recently begun to care about the color spectrum(adobe, srgb, etc.). Again generally higher is better.