Platinum and White gold are visually very similar, but both are distinctly different types of metal. So what are the differences and what specific advantages and disadvantages do they have in relation to each other.

Platinum.
Platinum is a naturally white coloured metal. Platinum will still have other metals added to it, however this will only make up 5% of the whole. Platinum is a denser metal than gold, meaning it is heavier, in fact almost twice the weight of 18ct. Both metals are rare but platinum is rarest meaning its price is a significant amount higher than that of gold.

White gold.
White gold is not a naturally found substance, but is yellow gold, mixed with derivatives such as platinum and palladium to give it, its white colour (nickel is also used in the united states), however due to the high instance of nickel skin allergy it is limited in its usage by legislation in the E.U. There are no set standards to the amount of these colouring metals that are added, however 18ct gold must be by law, 75% pure gold. To add a sparkly finish rhodium plating is usually applied to the finished piece. Rhodium is metal that is similar in colour to platinum which adds a hard, bright white layer over the top of the alloyed gold. This makes the gold look more even white, although over time this will wear away and the more true off white gold colour will show through.

Pros and cons
Platinum is a denser harder metal than white gold, however this makes it significantly heavier. As a result of this a piece of jewellery will be heavier than that of the same piece made in white gold. This can be a good thing as it gives a piece a more sturdy feel however it can also sometimes make other items feel too heavy and uncomfortable. The weight will also effect the price. Not only is platinum more expensive per gram than white gold, but also with its heavier weight it means the overall gram weight of a piece will approximately be doubled, thus giving a huge price difference between the two.
A problem for white gold is that over time the rhodium plating which makes it bright and white will wear away. This will mean that the white will eventually change into a more straw like colour. There are also varying qualities of white gold in regarded to colour. Good quality white gold will be a soft white and it is not necessary to have it rhodium plated. Cheaper poor quality white gold will have a distinctly yellow colour and will not look particularly white without the rhodium plating. The cheaper gold will look yellower as the whitening substances such as platinum and Palladium, due to their cost, will increase its price. Platinum's natural colour is white so it will remain this colour despite ware, however both will scratch and scuff.