git clone -b develop https://github.com/magento/magento2 .
or:
git clone -b 2.3-develop https://github.com/magento/magento2 .
It is the same, because the develop and 2.3-develop git branches now contain an identical code.
git clone -b develop https://github.com/magento/magento2 .
or:
git clone -b 2.3-develop https://github.com/magento/magento2 .
It is the same, because the develop and 2.3-develop git branches now contain an identical code.