Sway or antisway
 

People buy sway bars to take a curve well and keep an even ride in the curve. People buy anti-sway bars in order not to what? sway?

What is what? Everyone want a sway and some people want anti-sway. Why? If I'm not mistaken (correct me here if I'm wrong) they both give rigidity to the car and make it take a curve better.

I've seen some members complain about sway bars making you notice more the holes in the road. Is that true or is it their imagination?

What is the difference between a bar that costs $150 and one that costs $15.99+S/H?

If I were to buy the upper sway bar, would I have to get a better lower one? Overall, is it worth buying an upper sway bar?

I am not sure what a sway bar is! But an anti-sway bar will keep your car level at corners. There is no upper and lower anti-sway bars. I guess it is lower, because it can only be installed when the car is raised. The upped anti-sway bar, I believe is the same thing as a strut bar/brace. From your other question about the price, I am not sure if you know that S/H stands for Shipping and Handling. Therefore, your total price is $165.

I know what S/H is. I rephrased the sentence. Look above.