"My vote is for Singapore. If you want full enjoyment then you should select Singapore. You can enjoy shopping, many beautiful places which attract tourist and mouth-watering cuisine.
MALAYSIA without question. They are the friendliest, most accommodating people I have ever met.
Singapore ... you'll have more choice places
[Edited: 2013 Feb 26 08:44 - Rat on the Road:23681 - URLs removed]
Places to shop I agree but not of much cultural interest. Singapore is very clean, almost clinical in its appearance. Malaysia has much more to offer in my opinion, from wildlife, wonderful people to a delicious array of food
5 days is enough to cover both Singapore and Malaysia. 2 days in Singapore and then drive up to spend 3 days in Malaysia.
You can rent a vehicle+driver in Singapore to drive up.