I've never tried birthdaycakes.sg but we've tried 25grams. they do nice birthday cakes and cupcakes. we ordered a my melody carrot cake for our girlfriends birthday and also some pirate cupcakes for our guyfriends birthday. both times were quite awesome and consistent.
the baker was also friendly and professional about our requests. i think you can find more photos on facebook.com/25grams.
hope this helps! =)