I would go blood all the way , and yes their okay at 70 but other twinks like arcane mages, good rogues to some extent and hunters will give you trouble , they still hit very hard.Prot pallies............will make you wanna reroll their insanely op even up to 74.
I think the biggest attraction to prot pvp in general is that you can survive long enough to do damage against other twinks who don't have this survivabilty.
I loved pvp'ng as blood all the way through to 70, i had my parry at 20% at a time and would pop dancing rune weapon and lol at the numerous "clang" sounds id hear .
I tried 70 pvp but it was boring going against other twinks, plus the que times vary ,from peak to offpeak so if you are used to the lvl 85 ques these can be worse at offpeak.
Either way i really had alot of fun in BG's and would propably create another dk and take him to 70 just coz of the fun in bg's all the way there(lvl 60 pvp weapon can actually take you to lvl 66 , then switch to boa wep ftw)
(edit:i also cannot comment on their self healing versus at 85 since the highest my dk got was 70, i didnt take him higher than that)