Ext4 vs btrfs
Ext4 and btrfs are modern file system types which can be used with a Linux operating system.
 Ext4 advantages
Ext4 is the default for major Linux distributions such as Ubuntu. Ext4 is in use by a very large number of Linux users and has proven to be useable. BTRFS is not considered ready for normal (production) use, and has not been widely tested by end users. One of the primary problems with BTRFS today is its incomplete fsck (filesystem check) implementation, which may not be able to successfully fix file system problems when they appear. (According to the BTRFS wiki as of 2012/7/3, "while this tool should be able to repair broken filesystems, it is still relatively new code, and has not seen widespread testing on a large range of real-life breakage. It is possible that it may cause additional damage in the process of repair.")
Benchmarks have shown that ext4 provides superior read-write speed to BTRFS. Since BTRFS is under development, it may (or may not) improve performance to match ext4 in the future. Btrfs has shown high disk consumption on small files.
 BTRFS advantages
BTRFS will provide new features, such as the "copy-on-write" concept to improve performance and reliability. BTRFS systems will be able to "roll back", meaning all changes made to the hard disk since a certain point in time would be reversed.
 Developer Comments
Theodore Ts'o, principal developer of ext4, says that Btrfs is the way forward due to new features in its design.