I really like POS. I do. But there's an issue.. I won't go into the details, we all know what they are, but to break it down to it's simplest :

POS needs 1, just 1, TRUSTED number to start with, when you log in to the network. Then it's good to go (BASICALLY). However the POS coins wrap it up, NXT, blackcoin, DPOS systems etc etc.

That's the bottom line. Whatever ANYONE SAYS.

If you can handle that fact and don't mind, go for POS.

POW has flaws, yes, BUT there is no TRUST required at any stage. If this matters to you, POW is the only way to go.

For the most complete breakdown of the issues :

https://blog.ethereum.org/2014/07/05/stake/

and then

https://blog.ethereum.org/2014/10/03/slasher-ghost-developments-proof-stake/