What is the ideal baby formula brand out there for 7months plus baby? Now slowly letting my son to try friso stage 2. Whats the difference between the many brands out there?

My friend's son takes Aptamil Gold + AllerPro because of his allergies. I heard it's quite hard to locate this formula in Singapore so his father (who travels alot for work) would stock up whenever he can when he is in Australia/New Zealand.