The important difference between these two designs is that the classic “shared prong” setting offers a more secure hold for the stones on the ring. There is little to no chance of any of the stones being shaky or loose, let alone fall out of the ring.
The U-Prong setting for eternity bands has become very popular as this setting allows for the stones on the ring to be more visible. This means that someone looking at the ring from the side can see more diamonds than a regular setting.
Both designs are equally as nice and disperse the same amount of shine and light from the top. The main difference would be the side view of the ring.
It is more recommended to stick with a classic setting for bigger stones yet if the setting is done in U-Prong by a professional jeweler there are very slight chances that something may happen and you can still be at ease that your stones will not fall out.