NXT and Monero, these two are completely different coins and they cannot be compared IMO.
Which one has a better chance of becoming a successful alternative to btc/ltc?
I'm sure Darkcoin or(and) Zerocoin/Zerocash will overcome Bitcoin someday.
Why can two different coin technologies not be compared? What are the advantages and disadvantages of each tech?
Monero is maintained for anonymous transactions but it has some flaws in its code and other problems like being botnet raped.
NXT is the first pure PoS coin written from scratch. It brings asset exchange and some other features but suffers from unfair distribution.
Which one is better and how to compare them is up to you.
What sort of flaws have been discovered in the code for Monero?
I do know that NXT is mainly criticized for the initial distribution of it's coinbase. But if the technology is superior that doesn't mean that another coin based off NXT couldn't come along and solve that problem. If NXT's PoS system is superior to the CryptoNote PoW system that's vulnerable to botnets then that's a big plus for NXT.
NXT is a scam.
Those who get in on the "IPO" are the ones who always come out richer.
I think of NXT not as a currency....but as a platform to trade currencies, like Ripple.