Whatever suits your needs. I'd advise against Western Digital as I'm now 0/3 on their desktop drives (my 1 TB "green" drive is having problems 9 months after purchase, and now I have to deal with their sh!++y customer disservice once again).
For external, I'd go with a FW800 since that'll maximize your speed. Macally makes nice enclosures with internal SATA and FW800, but for some reason they do not daisy chain very well. I have a Rosewill with FW800, FW400, USB2 and eSATA in an aluminum enclosure (which are usually fanless) that cost $70 - quite a bit more than the Macalleys (which are also aluminum). If you need to move your drive between computers, be sure you have an enclosure that will work with all of them - minimally USB2.