I have only been to Singapore & hated it. DH has been to both & without a doubt would return to Bali & would not return to Singapore.

Maybe we just didn't go to the right places in Singapore but IMO there is nothing there worth seeing. Our hotel was crap, the people were rude, the zoo is a zoo & if you have been to a zoo, well you know what to expect, the botanic gardens are lovely, Raffles Hotel is just a building. A pretty building, but just a building. The city itself is very clean & pretty. We didn't really go shopping as we were heading to Thailand but we did wonder around a bit. Shops open late. We were there in 2007 for 2 nights.

I highly recommend Thailand. Lovely people, great food, cheap cheap cheap shopping. I loved Bangkok. It's very busy though. We didnt' have kids then so it suited us.

ETA: Didn't read all the responses but it looks like I've been outvoted lol!