There are trade offs, so no clear answer here.
First of all, just to be anal and clear something up ... what you have is actually a 4-ring and a 5-ring piston. The oil control ring at the bottom actually consists of two rings and a spacer.
The main trade off is, the 4-ring piston will have less drag on the cylinder walls, but the 5-ring piston will seal better. A better sealing piston will keep more power in the cylinder, but you'll see additional frictional losses. Most engines I've seen with the 5-ring setup are for diesel engines.
With the piston which is slightly domed, you'll have a slightly higher compression ratio. You'd have to do some measuring to figure out how much the difference would be.
I don't know if you are assuming the pistons are virtually the same or if you have the specs on both. One of the things you need to check is the piston height difference. To do this, place a single wrist pin in the pin bore on both pistons. You'll then be able to measure how much taller one piston is from the other. This will give you a better idea of how much one piston will stick up higher from the other. This may be important when installed, as the taller one may stick out of the bore above the deck surface or interfere with the head (I doubt it, but you should check ir).
One other thing to think about is the weight of the piston. The lighter one may have a slight advantage over the heavier one as it would be able to allow the engine to rev a little higher without fear of something coming apart.
