Rain gutter install question

Hello TW!
Just curious as to whether or not any of you have done DIY rain gutter installs? I've watched some videos and read articles about doing DIY installs and it seems relatively simple, I'm pretty handy around the house. My main question that I can't seem to find an answer to is this: Should I install the rain gutter on the "sloped" or "angled" part of my fascia? for example, above the garage and window on this house pictured below. My garage has this type of "A" shaped roof above it, should i be attempting to install gutter there? Or only on the straight horizontal part of the fascia?

 

Just the horizontal part.

Look around your neighborhood, you won't see any gutter installed on the sloped part. That's because there isn't any noticable amount of water falling off the side. The water all runs down the slope, which is why you need the gutter on the horizontal part at the bottom of the slope.

 

Thanks for the input!