I have a new 2TB external hard drive I will be using for additional storage and backup. I will only use it on two Ubuntu machines. Is it recommended to format the drive to ext4? Are there any advantages in doing so?
I think the core part of your question that is important is
I will only use it on two Ubuntu machines.
I faced the same dilemma as you and chose EXT4. The primary reasons I chose EXT4 are because 1) EXT4 will preserve my file permissions and 2) EXT4 better manages the storage of the data on it (e.g., it doesn't need to be constantly defragged and "coddled" like NTFS does). EXT4 is a more self-reliant file system than NTFS.
The only negative to using EXT4 is that you won't be able to access the data on it via a Windows machine. But as you said in your question, this won't be a problem because you are only using Ubuntu machines.
IMHO, the only reason to use NTFS is if you need to access the filesystem with Windows. If you don't, NTFS is really an inferior file system.
