The large fat bag is more versatile. You can get more height out of it or less, depending on how you orient it. The way they do the straps make it easier to get it over the rifle if you want to do that. And, the wedge shape is really useful on in a lot of ways. I used it as rear support on rounded things and as front support on a couple stages.
On one stage at LRSE, we had to shoot off a railing, then off an open barrel at an ~MOA target that was at 340 yards. So, you just had the rim to support the rifle on. I put the strap of the fat bag over the bipod legs (folded up) and sat it on the front part of the rim, and sat the buttstock on the back part of the rim. Then I just moved the rifle forward until I got the elevation I wanted. Was like shooting off a bench.

Ryan shooting that stage. You can see the blue barrel at the bottom of the stairs.
On another stage, we had to shoot off an a-frame at 390 and 790 yards. Everyone went to the top. I used the fat bag again on the front of my rifle and put the rifle across the second highest trusses and again just adjusted elevation using the wedge shape. Wouldn't have tried it without the wedge since I didn't know how much front height I needed before going up there.

Ken shooting the a-frame.
I used it as rear support on this stage and supported the front with the bipod. Wedge shape was perfect for this.

Ryan shooting the wire spool stage with the pump pillow on the front.
Wedge adds a lot of versatility.