BarF1

I have two 2.5 (40/80) both from Samsung, haven't fail me yet.  I am hard on them with many dls.
I have one 3.5 (500) from Maxtor, still running great as my storage bin.

If you need to take your HDD with you, 2.5 is the way to go.  You wouldn't want to haul the 3.5 + Power supply around.

My 2.5 weights in at 138g and my 3.5 + power supply weights 3lb + ...