I think it depends what colour pink you want. Irradiated pinks are a true pink, kind of vibrant. If that is the pink you are going for I would get the diamonds because they will sparkle more than sapphire. However, if youa re looking for a softer pink, I would go sapphire.
As for better, I like both rose gold and white metal with pink stones. But I also tend to like more muted colours of stones when setting with rose gold. So if I was going with the irraduated, I might choose a white metal, because those stones don't need any help looking pinker, and the contrast between the cool tone metal and the pink would be pretty.
Joseph Schubach Jewelers