The rooivalk was a competitive attack helicopter, but its technology has not been field proven, even in South Africa. There is also minimal field support for this helo.
The apache has been upgraded in the recent years and has an extensive track record spanning several wars, the rooivalk has not.
The rooivalk has been used by other countries, e.g UK, as a bargaining tool to get apaches from the us at a better deal.
My 2 cents worth