Let's see if I can separate the two questions:
1) Pucker factor. All three climbs are different animals, so they can make you nervous is very different ways.
Angel's Landing (AL) has a very steep drop-off and a narrow walkway, and from what I remember, the chain was only on the inside. Stepping away from the chain was the scariest part for me, but the trail itself is level due to steps in the rock.
Half Dome (HD) is steep, with a drop off directly behind/in front of you, and the rock is slick. But you are in the middle of a broad face with something "solid" onto which you can hold/clip in.
The MR Final 400 (F4) only really felt exposed to me when it was full of snow. There are ledges galore in the chute (when melted out) and the scrambling/walking between the ledges really isn't too bad. The most difficult spot, I thought was the entrance (in summer). It's about 3-4 moves of Class 3 on some moderately positive holds which are easier to grab if you're taller. There is also the crack nearer the notch, but I've only done that when there has been snow to raise the entry and then jam my crampons/boots into the crack.
Again, YMMV based on what freaks you out the most. For me, it's edges, not heights. Sometimes, even a 10ft drop will freak me out if I'm too close to the edge. I've heard of accomplished technical climbers (gym) getting sketched on the F4.
2) "DIfficulty" of the climb.
AL: 5 miles RT, the first 2 miles of the trail are paved (!!). Gain of <1500 vertical feet. Strenuous because of the steepness, but it ends quickly. Summit elevation: 5785 ft. (Plenty of O2)
Angel's Landing Description HD: 14+ miles (via Mist Trail), 4800 vertical. Short stretches of serious up, but great spots to rest and cruise (Vernal Falls, top of Nevada Falls, skirting Little Yosemite Valley, base of the cables). A full day, and the down can be as brutal as the up on quads and toes. Summit elevation: 8842 ft (higher but still quite moderate, can cause some difficulties if not acclimated)
Half Dome Info MR: Mileage depends on who you ask. Doug swears it's <4 miles, I think it's closer to 6. 6100 vertical, topping out at 14,500ft give or take 8 feet. While in snow there may be a boot track, and in summer there is a use trail, this is the Mountaineer's
Route, and requires some route finding as you trudge along. To me, this adds substantially to the "difficulty". Altitude plays a major role: you start just under the final elevation of HD, and climb to where rocks and marmots and birds like to hang out. You hit the scrambling section when you are both exhausted from slogging up from Iceberg Lake and exhilarated to be so close to the summit.
Wow, that's probably more detail than anyone wanted, but there it is...
-L
