I would suggest that you go with the third ring and there are many reasons for this. The first ring is simple and basic in design, but with lots of small stones instead of one bigger one. Always try to go for the biggest possible gem that will match a ring well, for example you don't want to go for a crazy big gem with just a sliver of a band for a ring either. The second ring is very clean and stylish in design, however styles and fashion change with time. Is it going to look as good in ten years time? Also, the way the stone is set doesn't look very secure to me.
The third ring has many things that work well, it is classical in design, never going to go out of style. The four prongs should provide a secure hold on the stone.
If you ever need to clean your jewellery, just use a tiny bit of toothpaste and the softest toothbrush you can find plus a little bit of elbow grease. This works for everything, gold, platinum and silver. EXCEPT for PEARLS!!!
Also, this being a scuba diving forum, I am going to say that pretty much most people here will have access to a ultraconic cleaner. That is what jewellery stores use so...
PS. For anyone interested the way to clean pearls is to use a little bit of mild detergent and warm water, soak a clean cloth in this solution. Just damp would do, you don't want the cloth to be dripping. Place the pearls on the cloth, fold the cloth over and roll it around gently between your hands. Next use a damp cloth, dampened with only water and repeat. Then place the pearls on a dry cloth on a table and air dry, no direct heat or sunlight.
