Which 50in TV is the best?

That is a very individual decision and difficult to say. I personally would stay away from budget brands like Hisense, Onn and others as there seems to be a number of complaints from those who have purchased those brands.  Others may say they are fine, but you get what you pay for with a cheap TV.  I would recommend focusing on a good quality brand TV that you can connect a streaming device to and not focus on the streaming features of the TV.  As other users have posted that when a smart TV breaks, you lose both the streaming device built in and the TV, whereas replacing a streaming device is cheaper to do when they become obsolete or break.  Usually, you can find deals on the good quality brands, (Samsung, LG, Sharp, Sony) on models that are a couple years old.  The best time for deals is around the time of the Superbowl or beginning of the year.