Imagine...
Bob has value (money or goods or cryptocoins...) and he want to give this value to Alice.

For Bob there only one private way to give the value exist: is to meet Alice and give value from hand to hand. Though it needs some conspiracy to remain private.

Any other way will involve the third parties like banks, posts or payment systems. Lets call them helpers.

This helpers can take value from Bob's hand and put it to Alice's hand. This is what calls transaction. Transaction holds such info as sender, recipient and amount. This info let helper to treat Alice as next sender for this value. Other words it lets Alice spend value next time. Any transaction can become private only if information about it is destroyed. And there is no such helpers who will destroy this information (think why).

Blockchain is same helper and it's advantages is that no one control all of it so no one can cancel transaction for the reason other than the sender don't have the value. Also no one can delete or change transactions.

Conclusion: for Bob any coin is best for privately give value to Alice until he not going to buy or sell this coin using his real ID or real IP.