Best practices for common code

What is the best practice?

Of all? Read up on the subject.

Google Coldfusion components

Adobe documentation on Coldfusion Components

Others say that cf components are fine to use on high volume sites, if written correctly. What is the best practice?

The best practice is to write CFCs correctly and to use them, wherever possible, on every Coldfusion web site. Why every? It is best practice to use the commonest CFC of all, Application.cfc.

The issue is a bit of a non-sequitur to me.  It's like saying "which is better: a car or a washing machine?" They're both machines,  but they do completely different things.

A component is an implementation of the OO concept of objects.  CFHTTP is for making HTTP requests.  Two different things.

If it's even possible to make a sensible performance comparison, CFHTTP is almost certainly going to be slower because it needs to make an HTTP request which has a bunch of network overhead, whereas instantiating a CFC is all done in memory (with an initial file system hit if it's the first time the CFC is used).

CFCs are not as performant as simple <cfinclude> calls, or probably even <cfmodule> calls / custom tag calls, which would be more sensible performance comparisons to make.  However the performance consideration is trivial compared to more likely performance considerations like poorly written code, DB and other external system calls... and... err... stuff like <cfhttp> calls...

The application architecture benefits of using CFCs greatly outweigh any performance considerations they might have.

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Adam