I have been a druid since wow came out. While I am an end game Resto Druid I allways level as Feral (ie TBC and WotLK) launch. I personally find feral faster with less down time, more survivability (bear form), better solo capabilities (again bear form for higher ranked adds) and also in my guild tanks are in higher demand for the 5 man instances during the leveling process.
If you plan to use instances a lot while leveling note that you are proboably best having either a cat/bear or Resto/Owl dual spec set up as tanks and healers are in higher demand for instance and while leveling the gear will lap nicely in those areas.
While even though I started WotLK with full SWP resto gear (throw some hit at it and it makes very reasonable owl gear) I found it easier getting feral gear. I beleive feral gear is much better itemised through leveling than owl gear.
To be honest while i would say feral, owl is not without merits, Some of the hardest things I have solod have been with a mixed balance/resto spec using CC and distance to kill them.