B of course it's more important. The security of trading system is one aspect. The key point is that the concept of "trading system" is also mentioned. It can realize the trading system and ensure security. Only when the trading system is relatively mature can it be profitable.

It is very important to make a profit in trading in A, but the key is that you have to make a long-term profit, relying on methods and execution.

Transaction speed and commission rate are not decisive factors.