5punk

You have Scent Fear (Survivors with less than 25HP are shown as 'wounded', less than 13HP are 'dying'. Both are asterisked on the map.)
Buy Scent Blood (The HP values and infection status of nearby survivors are displayed next to their name.)
Buy Scent Trail (Zombie is able to sense the new positions of survivors it's had recent contact with.)
Buy Scent Death (Zombie can sense the largest nearby groups of zombies and corpses, including members of its group, and distinguish revivifying bodies.) which one?!?!

scent trail is useful for finding people I found

okay. I want to finish up the nose skills

I'd say scent blood - it lets you know who only needs a few more hits before dying. And as you get 10xp for a kill it's most useful.

Have a look here, might help decide. I'd go for scent blood personally - I don't think I've ever seen scent trail work.

http://www.5punk.co.uk/phpbb/viewtopic.php?t=2256

I used it yesterday for the first time and it did the job