More energy efficient: writing in a SD card or transmitting by BLE for long period?
it depends :)  

did you think about the ble profile which you like to use? 

Do you have the possibility to buffer some samples in your MCUs RAM -- and then forward a block of samples to your SD or via radio. The most power will be saved if your MCU disables all peripherals most of the time AND your ADC runs timer triggert (CPU etc off) ... and if possible, you stay for several sec. and then handle the collected samples.

by the way, how much energy you have for the 10 hours?