I'm partial to the third one. It is unique and gorgeous. As far as platinum goes, i've heard mixed reviews. It dulls quicker than gold, and requires more maintenence. I told my fiance to spend more on the diamond than the band, so we went with 18k gold.  

I like the 2nd one. My friend has a radiant cut diamond and it is stunning! All the rings you picked out are beutiful. I am sure your fiance will love any of them. I like the 2nd one though!! ! : ) Good luck!

Well, this might not turn out to be that helpful of an idea bc I adore #1! Although #2 is a close second, both are gorgeous...I think you should look at the type of jewlery she wears and think about what stone/setting is what she'd pick out herself...Whatever you choose, she won't be disappointed!

My ring is platinum and I do think it makes the diamond shine a little more than white gold, no offense...I've actually heard that gold wears away faster than platinum and platinum is slightly harder so lasts w/o showing wear for a little longer...

 Well, at least I know I picked out 3 great options! Thanks for the input.

I hadn't heard platinum requires more maintenance... I've heard more of what runrgurl10 is saying: that platinum is more durable. I know white gold needs to be re-plated ever so often to keep it's white color.   

A thousand times over the third ring!!!!!!!! it is simple yet gorgeous! any girl would love it. Although i like the other two i feel there is too much going on with one and two. You want that one stone to really stand out and the 3rd's bands make the diamond pop!

It's beautiful and different. The first two look a little too "busy" for me.

Anyway, I work for a jeweler, so my knowledge might help...

Platinum - harder, pure white (diamonds just "pop" better), it does scratch easier than gold but you can polish it indefinitely and you wont lose any of the metal (with gold you do...) Platinum is 99% pure. So, if your girl has any skin allergies this is the way to go.

Gold - softer, with yellow obviously the diamonds don't look as "white", lose metal when you polish it...

White gold - more affordable, but it is plated with rhodium to make it the white color. After a while (6 months or so) you will have to get it replated. (Cost about $50-100 depending on ring style). White gold has zinc/rhodium, etc so if your girl has any allergies this will more than likely break her out.

Another option you might want to consider, palladium. (This is my favorite). It is extremely similiar to platinum. Yet, less popular. So, it's 60% LESS expensive! Based on my personal observation, the two are pretty much indistinguishable. the only real difference is the weight, palladium is a little lighter. And for palladium vs golds? The price is about the same...

 I like round diamonds, and hearts of fire are especially beautiful.  Plus, split shanks are very rare and gaining in popularity.  My second choice is number two.

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