I would like to have
GoogleDrive files offline on my Windows PC. I found two software that does that -
Backup and sync from google. Which one I should use and what are differences between them?
"Google Drive", when the client is installed on the PC, does synchronize any files to or from, the local hard drive's folder: C:\Users\CurrentUser\Google Drive\ (or, at least does as of August 2017.) @Ramhound reports that it was discontinued in July, so YMMV on installing it and using it long term. In any case, since this indicates it will not exist as it functions today, sometime soon, look for another alternative. Still, Google Drive while it still works, allows you to share a folder, and when the person you are sharing with closes that file in that shared folder, it will sync with your local copy automatically.
"Backup and Sync" from Google appears to be much more of a one way sync to Google's cloud, away from your hard drive. Then, if you want that file or folder locally, you'd have to "restore" it each time, to get the current version, locally. This means, if you were sharing a folder with someone, when they make a change to the file, you'd never see it, get notified, or automatically have a local current version of that file.
Google's new GSuite "Drive File Sync", that is available only to paid GSuite corporate customers, works similar to "Backup and Sync", however with one added "feature". They evidently put small "placeholder" files on your local hard drive, so when you try to open that Word file, IF you are online, it will "natively open a copy of that file", which first must be retrieved from the internet in the background. If you make changes to that Word file and it is still open, then I believe nothing is backed up to the cloud until you close it in Word. If someone else opens that Word file when yours is open, they will get the original copy, and not the copy you just modified, as I understand it. Nor will you have any notice that someone else modified it. There's also an "archive" feature available for admins, so they can "back up critical files, for instance, for preserving evidence in litigation."
Clearly, all of these Google sync tools are designed for use that optimizes native Google documents and not "files" as we know them, which are treated more as an afterthought and do not operated as a native Windows shared folder would. Unfortunately, features, pros and cons of specific programs will not be allowed to be posted here. Last I heard, since a solution for your needs might cause a debate and aren't considered "facts or solutions", suitability for your application is not a "solvable problem", products are only "opinions", and might be challenged.
Nevertheless here are features to look for, (perhaps this will survive in a past version of this post if removed). There are a number of sync solutions that will treat a local folder natively and share it with others. Most will first send it to their cloud drive, which means there's an extra copy "up there", which is a good backup. However, most have limited the number of versions that are kept or available. (Google Drive kept the last 100 versions for 30 days, forever if you manually "ask" GD to save a specific version.) This generally means there will be a delay in syncing large files, you'll have quotas and pay for space on their cloud, and you'd likely have other limitations. There are a few exceptions however, that are peer to peer. Resilio Sync is one of these that has no quota, no cloud, and is fast. However, the free version is for "personal use. Choosing any solution is difficult, because no matter what you choose, it will likely change, morph, disappear, or be acquired, after which you must choose and re-learn the gotchas once again.