How old do you have to be to decide which parent you want to live with?

i am sixteen years of age and currently residing in the state of Michigan although i am a resident of Pennsylvania, (which is where my mother resides) i want to continue living with my mother but my father has brought up the question of our "safety" living with our mother. he thinks my mom is an unfit guardian. she has taken him to court for child custody & support. this is the only reason my dad is now questioning our well being. we are completely fine living with my mother, currently i have been forced to reside in the state of MI at my fathers residence. i am very unhappy and homesick, the court is investigating our situation. i am wondering how long this may take & if i will have a reasonable say in whom i want to live with? any advice? i have also already written a letter to the court expressing my views and concerns.