I'd use spear over sword/shield in PVP every day for a ranger. However, sword/shield is definitely better (I've played countless rangers) until you get ranger spear and wilderness familiarity for tanking specifically.

I looked up spin. I could have sworn I've seen that it is skill based, however a post from Daevryn I see says "giants won't spin as well" so I'll assume that it is dex based now.

My giant staff spec tanked just as well as my human 23 dex did, but this may have been due to the higher parry rate of the giant and the inherent dam redux.

All that being said, the new answer is. High dex staff spec? staff/spear is better. Low dex staff spec or not a staff spec? sword/shield.