The downside of LCDs is that they tend to have less contrast between the lightest and darkest parts of the display, called the Contrast Ratio. In other words, when black is expressed, it is inconspicuous to describe real black. It consumes a lot of power because of the way it works. The disadvantages of OLED are that it is expensive because it requires organic materials to produce it. Over time, there is a higher risk of color-image burn-in.
Which should you choose between LCD and OLED? Both are good. LCD display technology is getting better, and OLED display technology is getting cheaper. What to choose depends on your taste and the size of your pocket. If you have a limited budget, only LCDs will work. This is because OLEDs can now be considered more expensive.