Frost or Unholy!? Spec for different Levels!?

I started playing DK a week or two ago. I've played Blood earlier but that was because I never cared about PvP since I was horrible at it. Coming back to WOW after 3 years, I'm more interested in PvP than PvE. I keep reading mixed opinions from people about Frost and Unholy but let's say I want to be strong in BGs on my own and not depend on healers too much.

Should I go for Frost or Unholy then?
Which spec is better for:
(i) Lvl 60-69
(ii) Lvl 70-79
(iii) Lvl 80

Also, for leveling, I know Blood is the best but since I don't have Dual spec, does Frost perform better or Unholy?

I'm currently Level 60 (I haven't been leveling; focused on making Gold) I've finally made 1k Gold. Should I go Dual Spec and start using Blood for PvE or save up for Lvl 70 Flying (5k Gold)?

[For Frost DK] Lastly, I've seen that 1 handed don't give str but instead, they give attack power. Does the amount of attack power given by them cover up for the lost str when switching from 2H to 1H? Does 1 str = 2 attack power?

if bg's are your focus be sure NOT to roll alliance

if your horde it doesn't matter what you pick, the guy your attacking will already have 15 people on him

in your situation i advice you to go unholy, frost for pvp is good but only if you have pocket healer, unholy doesnt rely so much on healers, doesnt have such big burst dmg but it can survive better and can do lots of damage in bg's, unholy is also better for leveling i think for higher survivability control and more heals