+0
Marvin is the tallest among/of all.

Hi,

Do both among and of fit in the above? Thanks.
+0
If you really want to know the truth, search at Google

on the BBC and the New York sites. You can do that by searching for:
site:bbc.co.uk "tallest of all"
(everything in the above must go into the Search box, in order to identify the site searched)
site:bbc.co.uk "tallest among all"
site:bbc.co.uk "tallest amongst all"
site:nytimes.com "tallest of all"
site:nytimes.com "tallest among all"
Comments  
For some reason, among fits better. I'm curious about what the natives think.
 Marius Hancu's reply was promoted to an answer.