Do I need to choose for a best responsed?

Although not an absolute must if you check your unresolved discussions you will notice discussions there are are considered pending discussions. But do keep in mind that although you do choose a best response and it removes it from your unresolved tab, they are not considered closed either as myLot TOS and FAQ does stipulate that discussions can be responded to at anytime during the life time of myLot as well. Good luck and wish I wish you a successful membership.