If you going to make 6 trips or more in Singapore, you should bought EZ-Link or Singapore Tourist Pass smart card.
Ez-Link allows to save 15% on a trip.
Also you can use Ez-Link for paying in McDonalds and 7-Eleven stores; for paying a trip on monorail Sentosa Express.
You can buy a smart card EZ-Link in a special ticket offices near a subway, bus stops and in TransitLink ticket offices. The price for adult 12 SGD (in this price have included price of smart card – 5 SGD and deposit – 7 SGD). You can top up your smart card in ticket offices, special vending machines, and in 7-Eleven stores.
Only one person can use smart card, but you can give it anyone for using.
When you leave Singapore you may return money(deposit balance) from your smart card, but you cannot return the price of smart card – 5 SGD.
Singapore Tourist Pass.
Using a Singapore Tourist pass you will have unlimited trips in Subway, Skytrain and bus.
The price of Singapore Tourist Pass: 8 SGD for 1 day + 10 SGD – the price of smart card (which returned when you return this smart card during 5 days after buying)
Using Singapore Tourist Pass you will have discount in McDonalds, 7-Eleven stores and vending machine with Coca-Cola.