vitalik buterin even had a discussion with devs on the nxt forum and came to agreement that nxt does not suffer from the flaws that other proof of stake does.. he also agreed the same thing about bitshares.. is it so hard to believe that PoS technology can evolve? 
https://bitsharestalk.org/index.php?topic=6990
https://bitsharestalk.org/index.php?topic=6990
That's not exactly what was said, or perhaps I'm mistaken. I think Vitalik mentioned that he would like to see code or a paper on the NXT solution (Economic Certainty) which is as far as I understand it a proposal at the moment.
There's some very clever stuff happening with NXT but at the moment there is also an air of mystery around potential solutions to the nothing at stake problem.
p.s. I hold NXT and BTC, nothing else.