I am writing an article that explains when to use **X** *instead of* **Y**, and when to use **Y** *instead of* **X**, that is the relative *advantages/disadvantages* of using one over the other given the situation. Now which one of the following sentences would be the best title for my article?

1. When should you use X **and** when should you use Y?
2. When should you use X **and** Y?
3. When should you use X **or** Y?
4. When should you use X **vs.** Y?

1 seems correct to me, but verbose. I have seen both 2 and 3 in many writings, and 4 only sometimes if at all. Which of them suits best as my article title?

I will happily accept any other smarter alternative, even if that completely changes the sentence construct.