Although I don't feel qualified to answer this, I'd recommend ext4. It just works. They are trying to achieve the one fs to rule them all with btrfs, but I'm not too sure how stable it is at the moment. It had a lot of issues in the past, and if you don't plan to use subvolumes, screenshots etc you're better off using ext4.

Fun story: I once had an issue where I couldn't do anything with my btrfs volume because it ran out of metadata space and I couldn't even tell it to allocate more. The solution wsa to grab a usb drive, format it with btrfs, make a volume group so more metadata space would be available to the filesystem, then make it allocate more space on the normal ssd. Everything was fine after removing the flashdrive from the volume group. It was a scary evening.