And how to know if what is the best altcoin to choose to have some profit?
Do some research on a particular altcoin that you want to trade with. Don't just follow what others are trading. More often than not, they are just feeding you for some speculations.
I can suggest to OP Better to go with bitcoin trading in LBC. LBC account can buy at market place threads, Post your topic at there as mentioned as you need LBC account and Start trading.
It really varies, sometimes the ads on there sell close to preev rates.
Or sometimes its at a all time premium high where you get fee of $40 minimum which you have to make up for which isnt feasible in my view.
The approach I think is this forum thread if possible.