Laptop computer help..

My old laptop took a dump so I got a nice refurbished one off Ebay. Seems very nice. Came with windows 10. What are all of you using for free virus protection? Is whatever comes with windows 10 good enough or do I need something better? On my last few laptops I used Avast free version. I really liked it but I believe it made the computer very slow..not sure so im leary of downloading it again without knowing. it seemed to do great on one of my older laptops but on my last one, it acted like I was using dial up it was so slow..If whatever comes with windows 10 is good enough, I will just use it. Im guessing thats what windows defender is? Need advice. Thanks!