depende unsa trip nimo.. if u love jewelries esp diamonds, daghan kaau didto nice mapalit nga cheaper jud compared sa other countries.. if u love to shop, then daghan malls didto ka shoppingan and daghan nice palitonon esp if naa sale.. hehehe
for nature trips, don't miss jurong bird park, botanic garden, singapore zoo and the night safari.. for some luge ride, beach photos, 4D, laser show entertainment, good collection of marine animals, then go to sentosa..
personally, if i only have 4 days in singapore, i would spend all of it sa singapore.. i wouldn't bother going to malaysia.. it's not worth the effort of goin there.. nice ra i.adto didto if naa jud ka extra time.. that's just my personal opinion
resources: my own personal experience.. lived in sg for 2 yrs and been travelling often to malaysia and other neighboring countries..