Depends on where on the wall they are.
As noted above....if it's likely that your going to be leaning a 4x8 sheet of plywood against the wall...put them about 52.35" high.
In the front of the garage, near the door....yea...14" to 18" high. In my case, all of mine are about 52" high....but at the front of the garage I have a big hook that one of my extension cords hangs on...so the cord stays on the hook, one end goes to the outlet, the other end I drag around as necessary.
Most of my boxes are 2 gang....and I flip flop the orientation of the outlets so that depending on how the plug is built, It's not sticking up...
And I have a couple of outlets hanging off the beam in the middle of the garage....I actually get a lot of use out of these....I have a short extension cord (12") that uses one of those plugs that allows you to rotate it anyway you want....it allows me to plug it in and it hangs straight down...the other end has three female recept's on it.
Note.....NOT the cord that is hanging down...that is why I made up the short extension cord....
You can never have enough outlets in your garage.....your not going to use them all at the same time...but it's a PIA to go searching for one....
Do this....open your door....walk in....where would you want to plug in an extension cord....that is your first outlet....
And....make sure you have a couple outside....
edit....looking at that last pic I think I just figured out a partial solution to my lighting in the front....I think I'll toss a couple of single tube T8's right on the header above the garage door so I can turn those on at night when the door is closed.