Hey, I was wondering which specialization is generally the most useful for the intimidate skill? Particularly for a human sized, low strength character?
And in what scenarios you could use the one that you recommend or tips on using them?

"Just Plain Creepy". Think Steve Buscemi from Con-Air.

Everyone was scared of that guy.

for physical, you need to hurt them, so probably not ideal for your char. but you can hurt people with words, e.g. threating, pretty well. that would be mental intimidation. if you're some kind of sadist and have knowledge about miscellaneous interrogation techniques, there you go. but you probably cant interrogate someony on-the-fly in a public bar.

i allways prefer the physical style with the Rorschach-enters-bar-scene in my mind.

Mental or interrogation would be your best bets. It depends on which comes up more in the campaign - someone who needs to be intimidated into doing something for the PCs, or someone who needs to be intimidated into divulging information to the PCs.