The one that you use and need.
Unless you just want to hold it as cash reserve and it‘s a depreciating currency (CHF historically is the opposite, so quite a good currency to hold at non-negative interest) or you‘re receiving interest well below market rates (Yuh doesn‘t pay interest on cash balances, do they?).
Looking forward to your next thread about how to cheaply move/exchange SGD to something else. 
As I understood your last thread about it, you don‘t want to invest these funds for the time being.
If you don‘t anticipate how you are going to spend it, and considering the time and effort you spend pondering about this subject, I‘d exchange to a currency that you can at least transfer easily and cheaply to somewhere else.