Choosing a water purifier starts with knowing your water. Municipal supply is usually low in dissolved salts, while borewell and well water can be high in TDS and hardness.
If your TDS is below about 300 ppm, a UV or UF purifier is often enough. Above that, RO is needed to reduce dissolved salts. A free water test at your tap removes the guesswork.
Modern RO purifiers can retain useful minerals and save more water, so ask for those features when you compare models.