I asked the same question some time ago about some companies' choices for different header sizes and logos among time. Some of my conclusions were that the choices were probably made because they wanted to:
- Communicate simplicity or they becoming lean (Remember Google's logo with bevels?)
- Save space to display the real value-proposition inside the fold (the first space on the screen perceived by a user when he/she enters any site), instead of the brand name, which probably hasn't acquired any buzz yet.
- Interfere not with the main-content (some sites even have no header)
As a reference, take a look to these sites:
- qz.com (try to shrink the screen to be smartphone size)
- fastcompany.com (mobile experience has a lot of areas of opportunity)
- The new twitter profile design performs a nice switch when you scroll down
The above examples made me ask: What are they trying to accomplish?
QUARTZ for example, has an excellent mobile experience, where the logo and header interferes not with the content. In the other hand, navigate through FastCompany's mobile site and experience how annoying the header results together with the top banners.
Twitter in the other hand makes use of the
window scroll events to shrink or enlarge the header accordingly.
Here's is a reference gallery on how web designers use logos, headers and browser events for managing the branding: onepagelove.com
As an answer to your question, I guess there is no a best size for the logo, I believe it resides on the project aims of communication.
- Is it an informative site?
- Is it an interactive site?
- Would a large logo interfere with my content or the size of the available space on the user's screen?
- Is the branding so important that it needs to be really present?
- Is it possible to integrate the company's branding with the interaction?