using a TV may or may not present you a number of problems from input lag, no support for 4:4:4 chroma subsampling resulting in very poor image quality (imagine a low quality jpeg file), ghosting, and low pixel density due to the larger pixels.
you could set the TV to PC/Game mode, turn off post processing features, perform an EDID Override Fix, etc. but there is no 100% guarantee it will work perfectly or reduce the problem to your personal liking.
some rule of thumb when choosing a TV as a monitor for gaming; the cheaper ones with less features (i.e; dejuddering, active contrast, SMART TVs) tend to cause less problems, Samsung has some serious input lag with their tvs as a PC monitor, and long hours of research and asking in forums helps.
if you're serious about a 120hz display, go for the monitor. using a 120hz TV is a gamble unless someone here can recommend you one out of personal experience.