AppleInsider compares 2017 m3 (1.2 / 3.0 GHz) MacBook vs 2015 m5 (1.2 / 2.6 GHz) MacBook:
Advantages of 2017 model:
Much better keyboard
Bluetooth 4.2 (instead of 4.0)
Faster RAM (same as 2016 model)
SSD overall twice as fast. 1.8X for read and 2.3X for write.
CPU 20-27% faster
GPU 44-50% faster
Throttles less, but partially because max acceptable temperature raised to 100C instead of 94C.
Longer battery life for video playback
Remember, this is vs. the 2015 m5 at the exact same base clock speed.