Either Blood, BotS, or Essence of Magic.
Blood:
Even with Blood you won't be able to contest a lane early game with most other demigods who get Blood. You will still lose the lane sooo :-/ it's not quite as easy to justify as other demigods. It's still a prefectly good choice, however, and pretty important if there is a Reg on their team
BotS:
Allows you to health-stack. However, unlike Beast, DA /still/ has a hard time with just BotS and no other mana item. If you get Unbreakble's it gets better but in some ways you still sorta need Plenor.
EoM:
Allows you to cast while oom (this is something you cannot do with BotS. You need mana to make mana, so to speak. And since DA really can't creep very well to regain mana with BotS you have to invest skill points in a shitty skill: Warp Area (exception: Warp Area is nice against characters who rely on a lot of AoE attacks since you can use Warp Area to evade it).;
However, BotS gives a better mana pool and EoM is /much/ harder to use than BotS. Stuns also kill you because the duration (3 seconds) isn't very long.
Build:
1. Spine Attack I
2. Demon Speed I
3. Warp Strike I
4. Spine Attack II
5. Shadow Swap I :ALWAYS:
6. Warp Strike II
7. Spine Attack III
8. Warp Strike III
9. SAVE
10. Spine Attack IV + Shadow Swap II
11. Warp Strike IV
12. Demon Speed II
13. Demon Speed III
14. SAVE
15. Shadow Swap III + Warp Strike V
16-20a : Elusiveness I - III + Demon Swiftness
16-20b : Precision I - IV
-
Play style:
You cannot rtb often. You cannot. You need levels to breathe. If you are rtb before level 5 you're doing something wrong.
If you go Blood you certainly will not have mana to spam attacks. This is why I put off getting many points in Warp Strike since you won't be able to spam higher levels of both of those attacks. Use Warp Strike as an escape device (use on enemy towers/creeps) or as a get-in-your-face against squishies. Also, the early point in Demon Speed lets you cap flags and harrass better.
You should basically be playing as a ranged character for the first several levels. Even if you get Blood you won't be able to melee for long without running and that means that they will just be hitting your back -> lose ~800 hp. This is espiecially true if you have BotS or EoM. Just use it and hit them with Spine Attack to piss 'em off.
The second you get Shadow Swap you should just start fake casting it to piss 'em off. Let them know you have it and will use it the second they overextend. This also lets you test their interrupt-ability if they are Oak.
Once you hit level 7 you should be paired with a good demigod, and preferably not laned against a UB. UB is, imo, the best counter to DA. Then just do your SS, then use Warp Strike to get back in their face. If they tend to "run on sight" of you and your showerbuddy, then don't start off with Spine Attack since the cast time of that will often let them get away out of range of Swap.
If you are a Blood build you should probably have something like:
Nimoth, Unbrekable, Vlemish, Plenor, Banded/Scailmail/Scaled Helm/Boots of Speed/whatever.
Sadly, you're an expensive build so you won't be able to contribute much to the team early-game. Make sure your teammates are aware of this and at least one of them is playing a cheap build.
Once Level 15 hits, rape face 
For 16 on, you really have two choices. AA becomes insane at end game and Precision is very nice when combined with some sort of artifact, like Mageslayer. However, Elusiveness also lets you evade the enemies AA/Artifacts (plus spit ) and the Level 15 "united" ability of Demon Speed and Elusiveness is quite nice. It really depends on yoru playstyle and how the game is going before you should decide.
Note that DA/Oak/UB is a very nice combination and in general I think DA works best with a UB on his team. Oak and Rook are also a nice choice. Not a quite so much synergy with Erebus or Sedna. Some synergy with Reg (mines) but you won't be able to hold lanes for shit with Reg/DA on your team so you will probably lose on War Score and since DA can't creep well... lose to giants :-/
