Since I'm not a single person I may not be qualified to answer this, but... My garage is at the end of a regular residential driveway that is just plain straight ol' concrete between the garage and the street. Consequently a vehicle has to move in reverse either entering or exiting. If I back out of the garage my vision of the street is more limited because I'm farther from the point where the driveway and the street converge. If I back into the garage there's less exposure to crazy drivers when I enter, and when I leave I have better sight lines for safely entering the street. It's all pure science.
Backwards science.
I particularly enjoy waiting (along with others behind me) for a guy stuttering back and forth in my parking garage while he tries to navigate the backing-in-to-his spot trick. Often takes a couple iterations to get it in there just right.
Here's the science:
1) On a scale of 1 being easiest and 10 the hardest, both pulling into or out of a spot forward is a 1. Couldn't be any easier.
2) Backing out of a spot is about a 4.
3) Backing into a spot is about a 9. I know this based on what I explained above occurring very frequently in my parking garage.
5 < 10
Science