User preference vs performance: Whats more important?

Studies show that web users don't always prefer things that work better. For example:

• Users tend to prefer icon-based interfaces, even where menu-based interfaces provide faster task completion.
• Users prefer text laid out at 55 characters per line, even though they can read faster at 100 characters per line.
• Users often prefer colored backgrounds, even though readability is best with black text on a white background.

So what's a web designer to do? In my opinion, it's usually better to go with what users prefer. After all, if they're not troubled by the fact that it takes a few more seconds to complete a task, why should you be? The most important thing is to keep them engaged. And that's best accomplished by giving them what they want.

Of course there will be exceptions. Where the performance differences are huge, and where task efficiency is very important, it's better to use what actually works best. But in my opinion, such cases aren't common.

For the most part, I'm going to continue focusing on user preference.