I am sure if you search through this forum and you will see some people are pro cow's milk and some against it, the same applies to formula. If I could decide what my son (16 months old) loves to drink I would have given him formula as I think formula are added with more vitamins and minerals which are good for a baby/toddler's development. However, some people may say formula is added with too much sugar and chemicals, not 'natural' so they go for cow's milk. However, some people will say cow's milk contain too much 'hormone' or is not as nutritious as formula. Therefore, it's all in your head and for you to decide.
Since my son turned one, he rejected formula completely. To me, formula tastes so yucky that I can turn my stomach upside down just by having a sip so I don't blame him for not wanting it anymore. I love cow's milk (full-fat). They are so yummy! And my son loves cow's milk more and more since I've introduced it to you about two months ago. As long as he is happy to cow's milk I don't bother much about formula. But, then again, I will stress more on the nutritions intake in his 3 solid meals because at the back of my mind II still think cow's milk lacks something the formula contains.