For simply keeping files synced between two computers, I thought Dropbox was the best.

Microsoft OneDrive is fuckin' awful in how long it takes for a file on one system to be synced to another, even when both systems are online at the same time. It also has a habit of completely pausing syncing entirely if it reaches a file it can't read (such as a lock file).

Google Drive works well, but I find its desktop client to be resource-heavy, especially on startup. I like its integration with my Android, though.