For the pin today(sunday, the pin is 11 yards from the front right of the green, and there are only 4 paces behind it, so the right is about 15 yards deep.
I think both holes present a unique mental challenge. For the 12th, the wind is the biggest factor in many players minds, as they may not be able to decide what the wind is doing, and therefore make a tenuous swing, most likely resulting in a pull over the left side of the green, or hitting it short into the water. The recovery from over the green is no cakewalk either as the water is still very much in your mind as you chip back down the slope. A lefty has an advantage at 12, as their misses mimic the shape of the green, but the mental factor is strong enough that im not sure how much of an advantage is there.
For the 17th, i think there is just a pure intimidation factor. The green is actually quite large, so there is plenty of room to hit the green with a variety of mis-hits, but the idea that if your shot misses the green there is no recourse, gets in so many golfers heads, and they try to guide the club, usually resulting in a poor shot that finds the water.
I am not sure which is harder of the two. A few pros certainly manage to make a mess out of each of them each year, so I would have to saw it is a wash. For the more accomplished player, the wind factor at 12 is definitely more troubling than the intimidation of 17, but if it is a day when the swing is a little iffy, both holes will definitely make every player stand over their shot just a little longer