How to answer this..........
Nothing beats real Foley. You have to keep in mind that Foley covers more than footsteps; it includes cloth (clothing movements), hand work (touches, slides, handshakes), fighting/impacts, kisses and many other human made object/other person interaction sounds. But it also includes enhancing explosions & crashes (debris, etc.), and creating unusual sounds like food impacting (i.e. in "Cloudy With A Chance Of Meatballs" hamburgers and other food falling from the sky) and all sorts of fantasy, sci-fi and horror sounds (magic, creatures, gore).
What has been found is that it often takes less time/money to create these sounds in real time with talented Foley artists than it does to have sound editors search through enormous sound libraries, then layer and manipulate them.
Now, it is becoming more common at the mid and low budget levels to do simple Foley, like footsteps, with samplers. You load in a pre-edited footsteps library and then "perform" the Foley by using a keyboard. This is a good alternative for those who do not have access to mics, pres, etc. and a space with appropriate surfaces.
But nothing beats the unique sound and feel of original Foley performances. You don't recycle exactly the same scripts, exactly the same shots, the same wardrobes, exactly the same edits, exactly the same score, etc., etc., etc., do you? So why recycle exactly the same footsteps and other Foley? The beauty of a new film lies in its uniqueness, including all of the sounds.
Great Foley is very subtle, vastly enhancing the characters and the story. Leaving Foley up to "machines" turns it into a video game.
