Definately Malaysia, had to show ours to get in, Thailand and Singapore, although Singapore is a law unto itself they have very strict regs on what vehicle are allowed in.
Any vehicle that can be slept in, camper etc is banned, in order to drive in Singapore you will need an ICP (Internetional Circulation Permit) which unlike all other borders isn't issued as you cross, you have to take a taxi or bus to the AA and buy one there before returning to your vehicle at Johor Bahru (Malaysia), you also buy your insurance at the AA, cost me $300 for 30 days,(easily the most expensive), then you can drive in Singapore. The taxi cost me $120.
Be very careful what you try to take into Singapore as customs are strict, chewing gum is banned, beer is heavily taxed etc and you cannot leave Singapore with less than 3/4 tank of fuel to go back into Malaysia as Malaysian fuel is so much cheaper.
Sorry to waffle on as you only asked about Carnets and here I am going on, you may be able to gather that I wasn't very impressed with Singapore and wouldn't recommend going there.
Lee