I've shot 5x7, 8x10, 5x12 and 6.5 x 8.5 a fair bit. While I like the impact of an 8x10 contact print, the whole plate size/proportion actually seems to be the best compromise of all of them. 5x7 is the most portable, 8x10 has the most "oomph", but whole plate has more visual impact than 5x7 without the extra bulk of 8x10. The 8x10 film holders are bigger, the lenses are bigger and heavier, and the cameras are bigger and heavier (some much more, some not too much more). It really does come down to horses for courses, but if I were forced to choose a single format without film availability being an issue, it would be whole plate. With it an issue, I'd choose 5x7.