Basing on experience...
Seagate is good as Paperweight. Very unreliable.
WD is very reliable, however, may new technology sila with the connectors which makes it difficult for you to change enclosures when needed. so hassle.
Hitachi, though konti palang nakakagamit sa friends ko, so far very reliable naman daw. Pwede na daw lumaban sa WD sabi nung friend ko.
Buffalo is nice, pero pricey. my brother has his buffalo Portable for 4 years na. still runs smoothly.
Samsung naman, 4 of my friends had their samsung HD crash on them. within a year. so... No.
Trancend, my brother bought 3 of these. 2 of them are not working in a span of 2 years, the third unit is still running after 4 years of abuse. siguro lemons lang nakuha niyang iba. pero still.
Bottomline, Hitachi or WD.