This depends entirely on your personal financial circumstances and goals – the real questions is: “Which duration is best FOR YOU?”
To answer this, start with what you want to achieve, and work back. There are lots of articles here on www.SavingsForNomads.com which will help you with the knowledge and information you need, as well as useful tips and advice, for you to make a detailed financial plan which still gives you the flexibility to live a fun life without feeling either restricted financially, or running out of money – so please have a look at them before you decide what’s best for you.
The only differences between the five durations themselves as savings plan options are that the longer the duration, the cheaper it is on an equivalent basis, as long as you stick to the plan, and the 5-year duration (only) has a higher minimum amount (200 per month instead of 100 per month on all the other durations). All five durations serve a purpose – which of them best fits with your financial goals?