Originally Posted by
kmart
On the flip side, you may find that your current ratio is too high and adding one tooth on the cog gives a ratio that is too low. Because 1 cog tooth equals about 3-5 chainring teeth, you have finer control of the gearing if you swap the chainring. Also chainrings are easier to swap than cogs, unless your cog is not on tight enough to begin with.
I wrote my original answer assuming that the person who asked, had made the ratio calculation already and found that +1 tooth on the sprocket or -n on the chainring was appropriate for his needs. I modeled my answer around that assumption.
After reading the comments written later on, this is what I conclude:
Striping of threads on hub as an argument against replacing the sprocket: this is a good point, but marginal in my experience. I have threaded plenty of sprockets and freewheels on an off and think the danger is minimal.
Replacing chainring because "it's usually made of aluminum so it lasts much less than sprockets made of steel". Well, this is not necessarily the case. If you use Rocket Rings, then sure, your chainring is due for replacement after 2000 miles. But with chainrings that are not made of butter, the lifetime is quite high, due to the fact that force is distributed on more teeth than on the sprocket. Chainrings are usually considered the part that wears the slowest. And if you have a steel chainring like I do on one of my singlespeeds, it will outlast a steel sprocket. Besides, we don't know what material chainring does the OP have.
As someone said: rotafixing off the sprocket is about the simplest thing in the world. Adjusting a chainring correctly is simple, too, but it requires much more work. Sheldon Brown has detailed instructions how this is done.