It's a matter of both really - Yes a shure SM57 will work great as a close mike, you must realise that a loud marshal turned up to 11 is really LOUD. On the other hand a condensor picking up the room ambience is also a good thing to do. Try putting the 57 up close 6" and the condensor about 6' away set in a fig8 pattern with the pattern set at 90degrees from the amp and blend till desired taste is achieved.
cheers
john