The 6x7 format is one of the best compromises you can make between the convenience of 35mm and the huge negatives you get with large format. Because you use more of the 6x7 frame than you do either with 35mm or 6x6, the usable size of your negative makes truly impressive prints, with almost the kind of detail and fine shading that you can get from 4x5", while preserving your ability to handhold the camera (at least for short periods). While I notice that most of the posts here have referred to MF SLRs, you might also think of the Mamiya 67, which is truly portable and yet gives you the enormous 6x7 negatives that are the main reason for getting into MF.