The WD is louder but will have slightly better performance.
The Seagate is damn near silent but a tiny bit slower.
Reliability seems about the same.
WD $175-225 for 100 to 120Gb.
Seagate $75-130 for 40 to 80Gb.
So, do you want a bigger, faster, louder drive for more money, or a smaller, slower, quieter drive for less money?