It really depends on your baby to be honest, from my experience every baby is different and reacts in different ways. For us, we started on SMA gold which made her constipated, changed to cow and gate, which gave her the most horrendous runs for about 3 weeks, changed back to SMA gold and she is now fine! So who knows really?!
It is best to give them a good try before you think about changing though, as it is apparently not good to change them too much.