Soft 404
Hmm decisions decisions.
Some of my early sensors for Arduino would have been a 3-axis accelerometer, like the Analog Device's ADXL345 sensor, and a 3-axis magnetometer sensor, like the Freescale MAG3110.
I seem to recall using the TSL2561 luminosity sensor quite a bit too. In fact I used these sensors in my very first design challenge back in 2014...
I think number of clones and high availability of counterfeit chips is good sign of popularity. For example DS18B20 is legendary chip in (not only) Arduino world. There is (very interesting) Github repo with investigations and Arduino sketch for detecting counterfeit including photos of dies 
