Older WD (from last year) is much noisier than the Samsung.
The later batches (this year, perhaps late last year) seem to be reasonably quiet in AAM mode.
Some Samsung with JVC motors have also been a tad noisier than the ones with Nidec motors.
So, if you get the best units from both, they are amongst the least noisy drives in their class (160GB modern drives, SATA or PATA).
However, the last time I checked, Samsung ran cooler and drew less power.
Performancewise I think Samsung takes the cake (read reviews to confirm, I'm working off my memory. The difference isn't that big either).
Personally I've now used 2 x Samsung 160GB myself for running up to two years (since they became available) and I'm very happy. No problems with noise or realiability with my two units.
However, I don't spit in the direct of WD either. I just ordered 2 x 320GB Caviar SE (WD3200 / 2500 year editions), just because Samsung doesn't have anything of comparable size.