The PL9823 is of particular interest to us as they are in the traditional 5mm dome type LED package and therefore can be installed easily in the light buckets that come with many 1/10 scale RC car body shells.
From a software point of view the PL9823 is compatible with the widely popular WS2812B, with the exception that the data format of the PL9823 is red-green-blue while the WS2812B requires green-red-blue.
The brightness of the PL9823 and the WS2812B seems comparable. However, a downside of the PL9823 is that even if it is not lighting up, it already consumes 7-8mA of current. In comparison, a WS2812B LED consumes less than 1mA when it is off. The 7-8mA is still acceptable for use in an RC car and won't hurt your run time much, but one still needs to take this into account when desiging a system around those LEDs.
The chart below shows the current used by the LEDs when set to white with different brightness values from 0 to 255 on the red, green and blue channels. The PL9823 current usage is ~8mA higher than the WS2812B at every level.