My vote is neither.
Well I have had a chance of using both products and let me tell you I have had bad experiences with both of them.
Bitdefender, I had a one year license so I installed it a couple months ago and when I restarted my computer it decided to intercept my WiFi connection and completely cut it off. So I opened it up and dug around the firewall settings and managed to configure it and get the WiFi back up and running. So I go to open up Chrome and browse away. I notice that web pages load very slow. Which I found quite odd cause I'm using fibre here in Canada. So I restarted the computer again to see if that solved the issue and I notice such a slow boot up. I then get so fed up with it within a hour or so installing it and decide to try my best to get into the control panel which took forever ,mind you. I go to click uninstall button and bam I get a BSOD, needless to say I wasn't happy at all with Bitdefender and ain't ever going back. I don't understand how they are constantly rated number 1 in detection and performance. Boggles my mind. Bitdefender has an amazing engine I give them that but the sad part is their software just has so many issues.
McAfee, this was actually the antivirus that came preinstalled on this laptop with Windows 8. Soon as went through the Windows setup and got tot the desktop and seen Mcafee I knew it wasn't going to go well. It basically slowed my computer down to a crawl and took ages to uninstall. At least it didn't mess up my internet or give me a BSOD when I went to uninstall it. It was much easier to uninstall than Bitdefender. I have heard Mcafee has improved their detection but however it still is known to slow your computer down to a crawl.
I'm now using Emsisoft Internet Security and extremely happy with it since it uses the amazing Bitdfender engine and it's in house engine. It's pretty sad how most of the products that use Bitdefender's engine are actually way better. Oh and don't forget Emsisoft's amazing behaviour blocker which I find way better than Bitdefender's active virus control component.