Any coin which isn't a flat image doesn't work for me. Someone just mentioned Coinwarz, and there will be many other instances that will require the coin logo once crypto is common place.

It will look odd in comparison to the rest.  

Here they are all flat - http://wheretomine.com/

Same here - http://coinmarketcap.com

And this was just mentioned - http://www.coinwarz.com/cryptocurrency

Yes there are a few 3d renders (BitBar, Spots etc) but 98% are just nice flat 2d designs, especially the coins.

This design as a flat coin and we might have a winner.

http://i.imgur.com/2PRUsuQ.jpg