The most important thing is to use a good freshly opened wine that you'd be happy to drink. If you use something cheap and nasty, then these flavours with be carried through to the final dish. The type of grape you use is of less importance. The reason it's often specified may be because some characteristics of the wine will still be present after the cooking. For example, the wine may be dry or sweet, citrusy, oaky, acidic, dark or light in colour etc.