They are the same. All babel-core/register does is require('babel-register'). https://github.com/babel/babel/blob/cb8c4172ef740aa562f0873d602d800c55e80c6d/packages/babel-core/register.js#L3
The recommended usage is babel-register since that is the module where the code actually lives, and babel-core/register has been removed in Babel 7.x. Better to depend specifically on the module you use, rather than load it as a side-effect of babel-core.