Which is the best formula for a six month old? Any suggestions?

I don't think there is a particular best brand; different babies react differently to different brands. Read the ingredients of each brand and see if there's anything that your child is allergic to. Otherwise if you are ensure, buy a small tin first and see if your child can accept it. My son is drinking Similac because KKH was giving my son Similac whenever I was too tired to breastfeed.