Comparison of their implementation does not make sense, because these are two different things: an alternative to IRb and a plugin to the first Rails console.
The Pry-rails gem simply adds an initializer to change the Rails console to Pry and adds some Rry related Pry commands . Pry-rails depends on Pry, and there is no reason why you could not use Pry with Rails without pry-rails, it will simply make it easier.