The best duration to choose is the duration which best fits with your personal goals and circumstances. Start with the overall aims and objectives for your savings – i.e are you saving up for something specific (in which case link it to that date), or is it for general wealth-building (in which case link it to how long you thing you will be earning money on a regular basis)?
In relation to the savings plan options themselves, the longer the chosen duration is, the higher the bonuses get and the lower the charges get. But this only makes sense if you have a realistic plan to keep it active – there is no point planning to be saving regularly from your earned income for years after you retire and stop your earned income.
Before deciding on a duration, have a look at the various articles on www.SavingsForNomads.com which are there to give you the knowledge and information you need to fully optimise your financial planning as a digital nomad, and use it to think about, research, and create your own financial plan which will make sure you turn your dreams into a reality. Then come back to thinking about which duration to choose – you might find that by then, you already know which one is best for you :-)