I would go for the following coins in this order:

Peercoin
Primecoin
Anoncoin
Quark
Tagcoin
YAcoin
Diamond

Criteria are:

- Innovative
(e.g. Peercoin/Tagcoin/Yacoin/Diamond have Proof of Stake, Primecoin serves science what gets it decent marketing, Anoncoin has the "anonymous feature", Quark might be the most interesting CPU coin)

- No Premine

- Active development team