Best PC interface for simple custom hardware

What interface of your PC do you use in order to connect to simple custom hardware?

The most commonly used interface was RS232 some while ago and today is probably USB, but wouldn't it be simpler for beginners to use the parallel port to control really simple circuits like step motors or LEDs? I have the impression from what I have read so far that the parallel port was not really designed for things like that, but I am not sure about possible limitations with respect to that.

Unfortunately, I can find very little literature on how to use the parallel port probably because it is somewhat outdated for professional hardware.

Does it make a difference for the decision on the most suitable interface whether I will just use output or also input?

I should add that I do of course know about Arduino, but I don't want to have any complexity hidden from me.

Moerover, I am using Linux and have a parallel port available. So I am currently biased towards the parallel port.