But, I can outline a few reasons, and this is from my perspective mind you.

First off, Humans.
Pros
Low XP pen, meaning you can pick on people lower level than you, as well as faster ranking. No vuln, can wear any gear a neut druid could.
four trains a level
Cons
Nothing spiffy

Wood-Elves
Pros
Wood-elf bonus to druidy things, high dex *better at dexy druid skills*, high int *Learns faster and I think this helps druid sups*, high wis *Saves against spells better and learns faster, also might help with druid sups*. Cool RP.
Cons
XP pen = slower ranking, also means you gotta fight people about your level and higher. *cept those fire ap's*. Low con, *Means people will send you packing a little more often* Iron vuln + not being able to pick up iron till you turn it into wood.

All in all they balance out, which is a reaccurrent theme in CF, so really its YOUR pick, I know what mine is.