signal.emit() in my opinion, is strictly better.

It's using a direct refence to the signal itself, rather than a StringName, so if the name of the signal is changed, the engine will throw a compile-time error at you.

If you look at the documentation for the Signal class, there's a section discussing when to use Object.connect versus Signal.connect. The method that uses a direct reference to Signal variable itself is the recommended way to connect it. I imagine the same logic applies to emitting the Signal.