Is it the Architect or the Specifier? The best I can tell, it depends.
It depends on when the selection is made.
It depends on whether more than one selection must be made.
It depends on what the product is.
It depends on the individuals making the selections.
Here are my thoughts on the subject. But I would like to hear yours.
We find that when required product selections become surprises or are delayed until the decision can no longer wait, the Specifier will make the decision. This seems to be because the Architect is fully engaged in completing drawings for a scheduled issue. His time is consumed in coordination and cannot be diverted to material selections.
The surprises are often caused by owners changing their minds, unexpectedly. This puts the Architect into a frenzied scramble to adjust weeks or months of work in a short time that was planned for other activities. There is little hope of controlling owner's decisions. Indecision is caused by many circumstances, but mostly inadequate information or little experience with a product type. Information and experience are controllable, given adequate time to address the issue.
For specifications requiring more than one product and manufacturer, often the Specifier makes the selections other than the basis of design. The Architects rely on the Specifier's experience with many products to know what will match the basis of design. This is a reasonable assumption when the product is a commodity item. If the product is custom or required to perform specialized functions, the Specifier may not be able to select alternative products, unless he was intimately involved in selecting the basis of design.
If a product is selected for its visual appearance, only the Architect is capable of determining what other products will be acceptable. Often there is but one that can offer the desired color, texture, and pattern. And that is the one the Architect selected as the basis of design. The Architect must make the decision. For aesthetic products, researching exact matching alternative products is a foolhardy waste of time.
When the manufacturer doesn't matter, don't make a product selection. Specify by reference standard or by description without naming a product. There is no rule that a manufacturer and product must be named.
Purely from my own observation of many individuals on many projects, the more creative the individual, the less likely a product selection. Why? Because design is never done. And the chance to find a better solution at a future time must always be available. Specifiers will make more decisions when working with creative people because someone must for the spec to be completed.
Now, off to decide the products to us on the next projects...