Easier method: use a cloud backup
You don't want to sort everything out, you say? We don't blame you for that. After all, we know the pain of constantly sorting your files, only to realise that you might have a duplicate somewhere in the system. That's wasted storage space and sometimes you just can't afford to lose even a few MB.
The key thing is to not care about whether that file you have is a duplicate. Rather, let the system sort that out for you. But more importantly, you don't want the hassle of manually transferring the files over. Instead, use cloud services such as Dropbox, Google Drive and iCloud.
The beauty with cloud backups is that you won't need to constantly check if the files are synced. As long as your devices are on a Wi-Fi network, it'll automatically sync with your preferred cloud backup.
More importantly, every file is synchronised across multiple devices. Chances are you probably own at least one smartphone, tablet and laptop, so that's three devices you'd like to sync your files with.