As above stated..also include a reason why.
I'm using on all my laptops where I have windows 7/8 on it , Security Essentials as its just the best in things of perfomance and also I think microsoft self knows whats best for their O.S
By the way, looking for my office for a new Antivir prog since Security Essentials won't be supported anymore for XP and we still have a bunch of XP's here. Should be lightweigthy , can be freeware or premium.
thanks.