Actually the stat distribution is not that bad, ATK and DEF are Dragonite's highest stats, so IV's have lower impact on those. If you are looking for an attacker, DB/DC is your best choice, specially if you like to dodge. With all honesty, I wouldn't invest candy in evolving the dratinis/dragonair you listed.
I don't evolve anything under lvl 20 unless it has over 90% iv's and nothing under 82% period.
To me the, I would take the DB/DC to a level where you are confortable attacking with him, I generally don't power up attackers because they already have so much advantage going into a battle that it's not really necessary unless speed is absolutelly crucial.
For me, Dratini candy is so rare, that I don't use it lightly, if dratini candi is easy to get for you, then by all means go for the highest IV dratini that you have