We find that very different quantum copying machines are optimal depending
on the indicator used to assess their performance. Several quantum copying
machine models acting on nonorthogonal input states are investigated, and a
ssessed according to two types of criteria: transfer of (Shannon) informati
on encoded in the initial states to the copies, and fidelity between the co
pies and the initial states. Transformations that optimize information tran
sfer for messages encoded in qubits are found for three situations: (1) whe
n the message is decoded one state at a time; (2) with simple schemes that
allow the message to be encoded using block-coding schemes; and (3) when th
e copier produces independent copies. If the message is decoded one symbol
at a time, information is best copied by a Wootters-Zurek copier.