Most white gold jewelry requires rhodium plating to hide the yellow overtone still present from the pure yellow gold after mixing with white alloy. I say most because there are now alloys that better mask the yellow overtone. These are not as yet used in the majority of commercially produced white gold castings and are felt by some jewelers to produce stiff and sometimes brittle castings. Conversely platinum pieces tend to lose their luster more quickly than their white gold counterparts and require skilled polishing. Regardless of whether the choice is platinum or white gold an engagement ring should be professionally serviced at least every six months to check the security of all stones including the center and to refinish or rhodium plate as necessary.
Platinum is denser than gold and therefore weighs more by volume. It also melts at a higher temperature, freezes more quickly and requires a higher level of skill on the part of the jeweler to work and set. Most shops that work on platinum are also equipped with laser welders which is an additional cost factor weighed by manufacturers.
Even when the cost per gram for gold and platinum is similar, a platinum casting will both weigh and therefore cost more. Additionally both 14 karat and 18 karat gold contain a higher percentage of alloy than platinum which is either 90% or 95% pure. This further affects cost.
For me platinum is equally at home when used in a simple, opulent sculptural mounting where its feel and weight are showcased and the open accessible surfaces are able to be easily polished to that inimitable luster as it is in a reproduction piece featuring the delicate filigree work of bygone years.
White gold really shines when used in micro pave or multistone pieces where durability and cost are priorities. As previously mentioned, while platinum is in itself extremely durable, its tendency to give under stress can lead to problems for those of us who are a little rough on our jewelry.