I think it's important to note that Warforged Power Attack costs all of 6 APs, whereas Halfling Guile and Cunning up to 4 each costs 20 APs.
I'm going to guess than when T3 of Ninja Spy comes out...it'll swing in favour of the Warforged a little bit, because of not being able to get all the Halfling Guile and Cunning.
Honest opinion here:
T2 already does. 3d6 SA damage? Why am I spending 20 AP for another 8?
I'm not, because I've already acknowledged that its a waste beyond t3 and I'm going to get other stuff instead.
Could not agree more, Aylin, and this is coming from somebody who prefers to play a halfling monk.
It really depends on what you're fighting and how you play. Against certain enemies you'll GENERALLY do more base damage with WF, and against others the sneak attack will put you ahead with halfling.
The easiest way to make the decision on race is plan out what YOU want to get out of the character. What feats/enhancements are a must. You aren't going to fit everything into a build, so decide what is important for you and go from there.
I'll note a few things though: the extra cost to your attack is VERY noticable while leveling up. While leveling it may be something you want to wait to invest into. Keep in mind WF immunities (with the exception of level-drain) are an overlap with the monk immunities. Also, 50% healing amp.