If Cardano fulfills all promises then it would be one of the best altcoin in history!
That's a big if, and if other altcoins fulfill their promise, they could also be the biggest in the market.
We don't really know, we buy a certain coin because we see its potential and time is very important, we need to let it grow as it will not happen instantly.
There's no significant movement on ADA so far, so that makes it a cheap coin right now.