first things first... everytime i want to play an MMO... i always look at its pvp system first... im kinda a pvp oriented player
after comparing the pvp videos between the 2 games... i finally decided,id go for DN
watched vindictus pvp videos and it seems like just a barbaric pvp... where in you just have to go near your opponent and hack and slash him to death or throw objects at him... or the one who can hack and slash more will win
... just from the videos i saw... i cannot say more since i didnt play vindictus (havent seen any stun, slow, evade, hit recover, counterattack skill mechanics in the videos... although knockdown/knockback is there...)
well ive experienced DN pvp and i can say its really good and fun... in order to pwn you really need to wisely use your cooldowns... time your combos and skill usage... also be quick to use evasive skills/jumping, hit recovering skills and counterattack skills in order to turn the tide of the fight if your being hacked and slashed/comboed... effective use of stuns, delay skills and knockdown skills are important too...
in the end... it comes down to " Preference"... both games are good