Basicaly "the most important person" is a very formal answer. Yes of course we can use it, but what i want to know is, do you want to write it down or just say it. If you chose the first one, i think yes, you can use the formal answer, it's pretty well. But if you just want to say it in your daily lives, i suggest you using this "you are the most important man/women of me (or in my life)" or " you are the apple of my eyes." etc.
the second answer, the "apple" one which i think is more oral more common.
wishes you can get your own answer. And Good luck to you guys. See you. bye