Zoom in... zoom out...

Zoom lenses are great. Depending on your subject, you can quickly zoom in or out to make sure that you're filling the entire frame, like you're supposed to... not?
You're doing it wrong if you limit yourself to using zoom only as a lazy replacement for walking towards or away from your subject. Yes, it is convenient that a zoom lens can do that. And in some cases it really works that way - think of using a zoom lens to capture a sports game for instance.

But never forget that a wide angle zoom lens will give a substantial different image than a tele photo lens; which means that there is never a real substitute for getting closer or further away from your subject.

Taking pictures of the same object with different focal lengths

Here's an image of a big rock taken at a local park.It's taken from quite a distance, using a 80-200mm zoom lens (and taken at 200mm focal length).

A few steps closer, and now the picture is taken at a focal length of 80mm. Can you see a difference with the previous picture? (Hint: there's a wall in the background!)

Now we're a good amount closer, and we're using a focal length of 50mm. The difference is clear: there's a black object in the background. But what is it?

Aah. It is some kind of tower. That becomes clear now that we're using a focal length of 24mm .

And another step closer. 18mm is as wide as my lenses go. But what a difference with the 200mm we started with!

So, which one is the best

The answer is of course: there is no spoon. Once you realize that all focal lengths are equal, but some focal lengths are in particular situations better suited to achieve what you want then others.

But it all depends on what you want to shoot, and how you want to shoot it. As a general rule: "environmental shots" require wide angle, "isolation" requires a longer focal length.