The coil with the most turns will have the higher voltage.
STEP-DOWN transformer
Secondary coil will have lower number of turns than the primary coil - the output voltage is lower than the input (less voltage produce, more current flowing in secondary coil).
STEP-UP transformer
Secondary coil will have more number of turns than the primary coil - the output voltage is higher than the input voltage (more voltage, less current flowing in secondary coil).
Equation:
V1 / V2 = N1 / N2
primary voltage / secondary voltage = number of turns on primary / number of turns on secondary