I keep a backup on one of my external hard drives, and one in the cloud.
I am not aware of cloud services losing or corrupting files, but I suppose anything could happen. You might want to discuss this issue in Google drive forums or Dropbox forums.
Please make sure you are also making regular and automated backups of your catalog file, using the Lightroom function that makes backups, make sure you check "Test Integrity" and "Optimize Catalog" when you perform this backup.
Well, the best option will be to use external hard drive. It is the easiest and quickest and cheaper way to maintain the backup.
You can always carry you data with you where ever you go.
I'm going with the external drive and cloud option.
Thank you both!