You're falling into the trap of "What would be good right now." This is a mistake when evaluating strategy. Any choice at this stage will necessarily be too late as it requires a time and resource investment that can't be made instantly. Instead I would suggest the following:
Void Rays take a long time to build and represent a substantial Vespene investment. This should allow you to produce as substantially larger army against a Protoss player focusing solely on Void Rays. A small investment in defensive structures will keep off a small force of Void Rays, however any larger force of Void Rays is better handled by direct assault on the Protoss base as you can produce a more cost effective force.
Bear in mind that a Protoss player investing in a gas heavy strategy (like Void Rays) will have an excess of minerals. The result is that their defensive force will largely be made of Zealots. Take this into account. Additionally, they are also very likely to expand as expansions are made out of minerals and provide excess gas very quickly.
Finally, I recommend better scouting. Seeing an early second Assimilator is a tell-tale sign of a Void Ray rush.
A word to Protoss players: A Void Ray rush is not a sustainable strategy, neither are mass Void Rays before you have a Mothership out. However, Void Rays do complement a Tier 1/1.5 force very nicely, especially armored units with High HP.
Since the last question was more about Void Rays I concentrated on more diverse Protoss Anti-Air
Gateway
Since Protoss strategies usually revolve around heavy gateway units, Stalkers are more or less a must in anti air confrontations. The most important rule of Stalkers is: unless you are chasing, never blink into battle. This is key, because as a tool, blink is far more effective as running away or chasing than it is as an opener. Stalkers are a very fast unit, so the only time you should ever feel the need to blink into an enemy is when they're running away.
Blinking away has two important aspects to it:
- Mass Retreat
- Moving the Front line back
While retreating is often times a necessary thing, it's the latter, that makes blink such an effective tool. When you find yourself against engaged in a battle, you'll usually notice that your vanguard (front units) take the brunt of the damage. If you blink them away as they take damage, the damage will spread more evenly over your whole force and your Stalkers will continue to do damage from longer periods of time.
Protoss Air
If your build is designed around Air units there are two important things to remember:
- Phoenix can shoot while they move
- Void Rays can shoot while they move
Most people don't know the second one. The key to any Protoss air confrontation is to make it a mobile one. This is why the speed upgrade for Void Rays is so crucial. Now Phoenix and Void Ray have different use cases, Phoenix are effective against light, and Void Rays against armored. Based on what your opponent is going you have to adapt. If you're seeing Muta heavy, go Phoenix. If you're seeing Viking/Corruptor go VR. In a PvP its usually whoever has better macro or more upgrades who triumph... you know, unless you get High Templar
High Templar
Usually built out of an early 4 gate strategy, HT are one of the most powerful units in the game. Psionic Storm needs no introduction, but don't forget about Feedback. Feedback has the unit property of being amazing against unexpected units. Allow me to list a few:
- Ghosts (no surprise)
- Infestors (no surprise)
- Dropships (wait what? healing uses energy?)
- Phoenix (how do you think they lift)
- Ravens (as well as point defense drones)
- Battle Cruisers (Oh yeah!)
- Corruptors
- Even Mothership
I have definitely had games where I won with just HT/Zealot just because of how versatile this unit it. What's more they can easily be transformed into damage soaks (Archons) to break Siege Tank of Void Ray lines.
Having trouble against Mass Void Ray? Strangely enough Psionic Storm is surprisingly effective against Void Rays. Because of the charging nature of their attack, many players won't immediately move their Void Ray out of danger.
Conclusion
As always, the key to beating a PvP army often lies in doing something unexpected while your opponent is doing the expected. Use Observers to try and retain the advantage in the game of information warfare.
Best Answer
There are a few things that you can do to kill a void ray rush, mass stalkers that target fire can counter his void rays. Just shift+right-click his void rays and they will drop like flies.
If you let him get that many void rays then it's your fault he wins, if you scout early that he's going void rays just 4 gate him. He will have a tough time holding against you. Most protoss players should have this build in their toolbox all the time, though higher ranked/skilled players will know how to hold it off properly.
Watch this video about Pylons & probes to be able to macro up effectively. Your macro can beat him straight up, even if he cannons in. Immortals destroy cannons so you can get a few of those and break him. Or you can abuse the fact that he only has cannons up front and use a warp prism in the back/side of his base and just warp in a bunch of stalkers and destroy the inside.
If he goes that defensive you can also abuse the fact that he won't be expanding and expand quickly. Get up another base quickly and out produce him. Because he's so heavily invested in static defenses he won't have a big mobile army. That means you can freely and for the most part, safely expand. Just make sure you know where he is at all times. A few observers outside his base can be very handy.