I prefer internal hard drives mounted in external enclosures.
X2
Internal drives usually come with a 3 year warranty. Externals usually have just a 1 year warranty. I've never had a drive die in a year...but frequently kill them before they are 3.
FWIW, I love the Western Digital warranty process. Super easy, and you can even have them send a replacement drive before you send them the drive.
Installing the internal drive into the case is about as difficult as legos.