Anonymity is indeed one of the Bytecoin’s and CryptoNote’s core features, but not the only one. However, narrowing the scope of this question down to anonymous transactions only, I’m confident that BCN offers the most advanced solution.
Something like that was said by one great alternative currency developer. And by the way, Bytecoin has caught my attention as being something a little bit different for three reasons: pedigree, anonymity. For sure, there are a lot of different currencies but as for me - the answer will be "BCN".