Before BBQ Pitmasters Season 1, it was RARE that we'd see anything other than pulled in a box, and then when we did usually it was a mistake (ala. didnt help the team at all). As Gavin said above, Brother Myron seemed to set some wheels in motion. Now I see probably 60-80% of boxes come across the table with MM sliced. Nice difference, but not completely necessary. Tom said it helps to have a variety, and I tend to agree with him. However, a really good tender pulled-only entry can do just as well if not better than another entry with MM sliced.
However, all of this could be very regional as Todd said. Sliced chunks tend to not play well here at all.
One thing I do know is that things change. What works well for a few seasons in one area may not work well a few years later.
Me, as to what do I, as a judge, prefer? I prefer perfectly tender meat seasoned to perfection.