The other consideration is you may gift Silver or Gold to a family member depending on whether they'll be traveling. By definition, they are not heavy travelers or they'll achieve the respective level themselves. If they are not traveling, there is no point in gifting them the particular level right as it becomes available nor towards the end of the period since it'll only be active through Jan 31. If you reach PM or DM early in the year, you may chose to gift the level right then or you might need to wait until Feb 1 if the recipient is already at the "to be gifted" level since Delta won't allow you to gift such level until the recipient is no longer at the level.

So, as the person deciding on what to chose - gifting the level, taking a travel voucher, or going for the RDM miles, you can wait and make a decision later. As the end of the period expires, you go for either a travel voucher (which has an expiration date) or RDMs (which don't expire on your account).