I've never been happy with a sandwich that I had to use a fork and knife for... it seems too proper!
I've also never been fond of sandwiches that spill thier fillings on me while I am eating them- having to clean up afterwords makes it lose some of its convencience.
I liked the simple Brazilian steak sandwich that I was often handed by the maid on the way out the convent door- a slice of steak between two halves of a bread- delicious and perfect

(the Brazilians used bread more similar to what would be called a roll here- it was smaller, so you would simply slice it in half and put your sandwich filling in the middle!)
And a sandwich with a good beer is heaven!