How to read speaker sensitivity rating?

Neither, the modulus of impedance vs. phase angle determines ease of drive, sensitivity has nothing at all to do with it.

The 102db speaker will play louder, and as a rough, perceptual estimate, every 10db increase in loudness makes a speaker seem like it is playing twice as loud.

Viridian also noted that phase angle will make a difference and maybe more than impedance magnatude. Of course, the amp killer speakers, no matter the sensitivity, have low impedance and adverse electrical phase angle in the upper bass, where much of the energy is. They are the gas guzzlers of the audio world and will suck current out of an amp like there's no tomorrow.