This is theorycrafting. I have not played the Demon Hunter (or any classes) yet, and I know that all the classes will surely be changed in some form before final release. This is my take on the current Demon Hunter from a theoretical perspective and why its build options are much narrower than they appear.
Let's start with the tl;dr for those who want to skip straight to the point, because this is going to be long.
tl;dr: Evasive Fire is the only reasonable choice for your primary hatred generator.
How did I get to that conclusion? Let's start with what role your generators are supposed to be filling.
Why use a generator?
Hatred generators are utility spells, really. Your damage is going to be coming from your spenders. If the generators dealt as much damage as the spenders, why would you ever bother spending hatred? To entice you to spend hatred, the hatred spenders are, well, better. That means that hatred generators should be good at generating you hatred to spend on your big spenders, and to keep you alive long enough to actually get off the heavy hitters.
What about my other favorite generator?
Hungering Arrow: Hungering arrow is decent single-target damage. With runes, it can be made into decent single-target damage with less-than-average AoE. It does nothing to keep you safe, no matter what, and generates less hatred than Evasive Fire.
Bola Shot/Grenades/Spike Trap: These are not bread and butter skills. Yes, they can serve useful functions, but their delays prohibit them from really being amazing spammed abilities. They are all about damage, and not about utility. They do not serve the purpose of a primary generator, although they can be good as situational backup generators.
Entangling Shot: It doesn't generate as much hatred as Evasive Fire, right off the bat. It doesn't deal as much damage as Evasive Fire. Even though that's not a primary requirement of a good generator, it is nice to have. The utility granted by Entangling Shot is not good when used in quick succession, while Evasive Fire's utility is. Entangling Shot is the second best Demon Hunter generator, but it is still completely outclassed by Evasive Fire.
Strafe: Strafe is all kinds of bad. It still technically costs hatred, despite being in generators, but it doesn't have the damage output of the spenders. You still gain hatred while using Strafe, but it's slower than your passive regeneration. This means that, as far as damage output is concerned, you're better off using any hatred spender. As far as hatred regeneration is concerned, you're better off using any other hatred generator.
Yes, you can kite a bit with Strafe, but not as well as you can with Evasive Fire. And you're not gaining as much hatred while you're doing it. Strafe is outclassed by every single other Demon Hunter skill.
What makes Evasive Fire so special?
It is the best of all the worlds of all the generators. It keeps you safe, its utility is always useful, it generates the most hatred, and it still maintains decent damage. You can use it to automatically kite while recharging hatred super-fast and getting back to where the real action is: your hatred spenders.
Please post constructive comments only. Please feel free to prove me wrong with your well-thought-out Demon Hunter builds that don't include Evasive Fire. I want to be wrong in this, but I've thought about it quite a lot and can't seem to figure it out.