In GSM which frequency uplink or downlink is greater?

The main reason of selecting a lower frequency for up-link channel in GSM is because of free space path loss. The more is the frequency the more is the loss.

As mobile phones, being a battery driven device, have limitation in terms of power we should always look for lower path loss. Whereas BTS antennas can transmit the signal (in down-link channel) with a comparatively high power, which will compensate the path loss.

And that is why it is chosen to have lower frequency for up-link and higher frequency for down-link in GSM standards. The same theory applies in almost all type of radio communication.

NOTE: Frequency and power are independent of each other. For example you can control the transmission power of BTS antenna, which still transmits in the same frequency.