I was in my local art supply shop today, and they stock the Staedtler Lumograph, a pencil I've seen recommended a couple of times. I bought one, and here's a quick comparison with my current favourite Faber Castell 9000 (both pencils are 2B grade);
1) The Lumograph has the darker line - the Faber Castell is a noticeably lighter colour side by side.
2) The Faber Castell blends/smudges more easily - a series of vertical strokes is easily blended into a smooth patch of grey - the Lumograph strokes are still somewhat visible even after quite vigorous smudging.
3) Here, at least, the Faber Castell is cheaper (between 10 and 20 pence cheaper, depending on where you buy).
The difference between the two pencils isn't enormous, but the Faber Castell 9000 is the one I like best - it's slightly smoother, and I like the ease with which it blends. The Lumograph seems to hold a point better, and I can see that its dark, tenacious line could be useful on occasion.