I used to have 4 as my favorite number, but now it's 7 mainly because my favorite movie has the number in the title, but other than that I don't know why it's my favorite number. Close second is 12 because I won a big chocolate bar on that number!
0. It's the most powerful number ever. Everything is valueless without it and it also can make anything valueless. It also can create infinity when you divide something by zero.