- security: The drive offers AES. dm-crypt offers your own choice, if you're not satisfied with AES. Both can be erased very quickly by erasing the key.
- convenience: both methods will prompt for a password once, at startup; although you could store the LUKS keyfile on an external device, e.g. a USB memory stick
- with dm-crypt, you have the flexibility to only encrypt parts of your system, e.g. only the /home directory (when put on a separate partition)
- recovery: if you forget the drive password, you're busted. For LUKS, you could (depending on the level paranoia you want to accept) have multiple copies of your key. Printed on a sheet of paper, if you want to. Or hidden inside a book. Or ...
- Both are not dependent on the surrounding hardware, so your disk can be recovered even if the original laptop/PC dies.
- performance: the device built-in encryption should be mostly transparent, so I assume almost no overhead. With dm-crypt, your CPU does the en-/decryption.
- Also: In linux 3.1 and up, support for dm-crypt TRIM pass-through can be toggled upon device creation or mount with dmsetup. So you need to take some steps, but TRIM is supported.
To summarize: the built-in encryption is the fast (runtime and setup) and convenient option with no frills. dm-crypt/LuKS offer many more options and features, but is more time-consuming to set up and reduces performance somewhat.