^ this! Dfs has better all around defensive bonuses, whereas dragon defender has better offensive bonuses. Not that this is a CHARGED DFS included in the picture:
If it's a wep like korasi the spec is less effected by the attack bonus and more the strenghth but if it's like a vls or somit else a bit of accuracy never helped and 1 str is nothing big.
yea it also depends on what your doing, i only use my dfs on dragons. If I had high enough herb (which i'm working on atm ) to use super antifire potions i would use dragon def. for everything and sell my dfs. But it is true that dfs has a way higher def bonus.
A charged DFS is much better mainly because of the def bonuses it offers. Also, i think the dfs price will crash seeing as though yuo can get visages/dfs's whatever from barrows now.
I personally use a dragon defender when i'm training slayer, because it provides attack bonus which makes you hit more accurate. DFS i'm only going to use for other things such as pvm/frost drags.
So they're both useful, in the end i'd say Drag def would be best/most useful
If you have a good camping method like Unicorn or Soul Split, there's no reason for a DFS at all. Dragons are all weak against Stab, so even against dragons the attack bonus of the defender is much better (as long as you use an Antifire/Super Antifire).