Which is the best cryptocurrency exchange on the market?
This is hard to tell. How do you measure the quality of an exchange?
There are quite some points which have to be considered. Like security, pairings, fiat gateway, availability, UI, etc..
Seems there is out some system, which are using many exchanges - like Bittrex, etc. Many seems very similiar.
Exchanges do not all run the same system. Each (probably) has been coded only for the specific exchange.
Do note that running an exchange is not a plug & play project. A lot of exchanges has been exploited (and funds stolen) due to low security measurements.
Can you maybe mention some exchange source, which you think is preatty good. I can pay for code as well with reasonable price.
You won't find a reputable source. If you do find something, be prepared that it contains security flaws which could lead to the loss of your whole hot balance.
If you want to get it coded properly, go and look for a trustworthy development team. I would not consider asking random stranger on the internet for such a task.
Be prepared to pay several thousands of dollars to get a properly working exchange running.
