I didn't look too much into NXT's asset exchange, so sorry - maybe someone is more knowledgeable there.
You are doing it bad Sukrim. Just look here:
http://coinmarketcap.com/assets/NXT AE is the most used and successful asset exchange by far.
Uhm...
http://www.ripplecharts.comRipple "assets" mostly are currency balances though, not share ownership of a company or project, so I'm not so sure how to compare these.
Anyways, I don't really want to argue about trading volume or how to measure "most used". I simply stated that I don't know exactly how NXT's AE works internally (colored coins implementation, baked into the NXT protocol, explicit/implicit offers, automatic margin trading bycked by NXT themselves... there are many ways how it might be implemented).
You also didn't explain how it works, only that it gets used, apparently successfully.