Are wordmark logos more effective, or brandmark logos? We see companies like Coca-Cola or Google who are doing fine with very effective wordmark logos, while companies like Apple rely quite a lot on their logos initially.
(I remember reading an article talking about how the glowing Apple logo on the back of the Apple laptops was one of the most important forms of advertising for Macs initially when they weren't as popular as now.)
I assume by "brandmark" you really mean a brand symbol/icon. If so, then the answer is "yes"; both word marks and brand symbols/icons are more effective.
Each have their place, and a logo designer or brand marketer can't afford to exclude either from their repertoire.
Would Apple still be Apple if they had only a logotype? Could you imagine IBM as IBM if they added an abstract or pictorial symbol to their brandmark? Should the New York Times print a giant icon on the front page of their newspaper instead of the wordmark they currently use?
Asking whether all logos should be textual or graphical is like asking whether it's better for a logo to be red or blue. The appropriateness of any logo design choice is relative to the brand it's supposed to represent. So what you should be asking is "would a wordmark or a symbol/icon (or both) be more effective for conveying my brand?"
This is a subjective question, so I don't really know if there's an answer. I think the context of the mark is really what's most important.
Think about the new proposed Starbucks mark. They have relied on their word mark in the past to create a brand recognition for themselves, but are now so recognized that they can remove the word mark and just keep the image.
I think the most effective marks are ones that combine type and image, but the effectiveness of the mark totally relies on the brand of the entire company, eg. the product, the services, the way the company communicates, etc. The mark just represents the perception of the company in an image.
I think that the word logo is relatively easy to remember but, the logos that are just pictures have a bigger impact on people. I think that the word logos just take a while to get comfortable with when you first see them. I do believe that everyone has a different opinion.
