This is a topic that we could all discuss for time indefinite and still not agree on one logo that would be classified as the best logo of all time.
But as with everyone else here, I have an opinion as well
To me what classifies a good logo is what impact it has on the environment it is in through time.
This doesn't mean that a logo has to have a long history to be a brilliant and effective logo, but it helps.
An example is the Google logo. Google has only been round for just over ten years and still, anyone who knows anything about internet has most likely heard about it and also use Google as their main search engine.
Google is a strong logo, but then again it has not proven itself for more then a decade, so a logo that has survived the test of time would be considered as a stronger logo in my eyes.
Texaco and Shell are two good examples of this. These two logos have been round for over a century and are still as strong as ever. They have a good development as well and as history has shown, every re-brand that these two companies has done has fit the time they have been designed for.
Who knows where Google will be in a century? It might still stand as the most recognized search engine logos, but then again, with technology evolving as quickly as it does, it might not be. Texaco and Shell has at least shown its strengths with a great history.
With all this said, my ultimate logo must be Coca Cola. As much as I hate the drink it has stood the trials of time since 1885 and is still one of the strongest logos and brands in the world today.
Thanks for reading
D