If you are not concerned about being able to recover data, a simple quick format would work. But that would allow for data to be recovered from the wiped drive. If you want the drive wiped clean with minimal chance that any data could ever be recovered, it will take time as the software (both GDISK and WIPE) will over-write each sector several times. The larger the drive, the longer it will take.
Also, please remember, even GDISK or WIPE do not guarantee that data will not be recoverable. The only true way as per DOD guidelines is to destroy the disk.