hmm.. I think each baby will react differently to different brands (e.g. due to taste or perhaps baby is sensitive etc). I have a friend who supplemented her breastfeeding with formula. She had to try a few different brands before finding one that her baby takes to. For her, because she only started having both breast milk and formula milk when baby is past 6 months old, she was able to get samples from the various brands.
If I'm not mistaken, most companies do not offer sample for stage 1 formula (but you can try contacting them to request for it I suppose).
Here's the link for Enfamil:
http://www.enfagrow.com.sg/get-your-free-sample-now-sg