Choosing a new mountain bike
 

Hi I am writting from Colombia, nice country and many trails to explore.
I want to buy a mountain bike for maximun 600 USD, front suspension is OK.
I have heard that mechanical disc brakes are not very good, some people prefer to have V-brakes. The say that if you going to buy disc brakes, the system must hydraulic. Is it true? Because it is much more expensive
I am looking the following bikes: Specialized p. All mountain 1 USD 590, trek 4300 disc USD 599 y la felt Q520 por USD 559. Any Ideas?
Advices appreciatted.
Jorge