For the record, over here most people used to go with the 'British' one until fifteen years ago or so when the notion that this was 'wrong' and we should say NY-KEE instead became widespread. I guess nowadays both are frequently used - like in most cases where American and British English differ.

Agreed on the comments above regarding Adidas - but while we're looking at the origins of the brand names, it makes one wonder if the Brits also pronounce the goddess Nike's name that way? Wikipedia has only the 'American' pronunciation on its page about the goddess, for what it's worth.