There are definitely differences. Some hog system resources (AVG and Kaspersky), some cause other problems with applications (McAfee), some are lightweight but don't do an exceptional job at actually detecting/stopping viruses (Windows Defender).
Of the free options, I used to use AVG but it started to really slow down my PC so I've been using Avira recently. The only thing that I don't like about Avira is that it has a daily nag screen, but it's free so I can't really criticise them for trying to pay the bills. If you want to give it a try: https://www.avira.com/en/avira-free-antivirus
ESET NOD32 is also good, but it's not free except for the trial.