First of all you buy TV for once i.e. minimum of 5-8 Years you are not going to change tv so, dont go by price i.e. for the cheap prices!
If you want to compromise with the price then go For Micromax and Vu LEDs selling best at the budgets!
now you should consider the things such has the newest technology in the TV nowadays there are android tv, OLED tvs, Curved displays tv, etc
optimum You should buy a TV with minimum resolution of 1080p and should have 5.1 channel surround sound also TV should have the connector ports like USB And HDMI ports!
Now when you visit the Showroom you should compare the TV panel’s with your Eyes not by the company name . the visual setting should be equal while comparing this lets you to get the best of available TVs!
To consider the screen size you should not think to buy a big screen but the screen size suitable to the place or the room where you are placing the TV!
See My advice is that dont invest your money Buying the Smart TV instead Buy a GOOGLE CHROME CAST , connect it HDMI port and make any of the available TV a smart TV!