Which is the Highest Downlink Power Cell Phone Signal Booster?

Among other non-technical considerations such as budget, sq. ft. coverage needed, etc. - Amount of "Downlink Output Power" and "Gain" should both be your main considerations when choosing a signal booster. Greater Downlink Power and Gain are important, but in different situations as detailed below.

Highest Downlink Power Cell Phone Signal Booster.

Downlink output power is measured in Decibel Milliwatts (dBm). It indicates how much amplified signal a booster can re-transmit inside. The max downlink power sets the limit on inside coverage area when amplifier has enough signal. Thus when outside signal is strong, you should get the booster with highest Downlink value which will provide maximum coverage inside. The reason for this is that if you have good outdoor signal (-80 dBm RSRP or better such as -70 dBm, -60 dBm, etc.), your signal booster will be downlink strength constrained because you're quite likely going to reach the max downlink output power of the signal booster.  Thus, a higher gain power cell phone booster in this instance would be of no benefit. An example of the highest downlink power output cell phone signal booster you need would be this booster kit with up to 16.6 dBm Downlink Power.

Highest Gain Cell Phone Signal Booster.

Gain is measured in Decibels (dB). It indicates how much a signal booster can amplify the signal that it gets from exterior antenna. When outside signal is weak, you should get a booster with highest Gain output capability. The reason for this is that if you have low outdoor signal (-90 dBm RSRP or worse such as -100 dBm, -110 dBm), your signal booster will be gain constrained because the downlink output power limit will never be reached. Thus, a higher downlink power cell phone booster in this instance would be of no benefit. An example of this highest gain cell phone signal booster you need would be this booster kit with up to 100 dB Gain.