I have to say for a cheddar sandwich I prefer the sharpest cheddar available because it's just awesome. Then I like to take some honey mustard (definitely sweet not spicy mustard) and just spread a bit on the bread. Preferably whole wheat or something like that. A bit of lettuce is nice too, and any sort of sliced meat that isn't too overpowering or spicy. Oh and thick slices of cheddar are where it's at!

Enjoy!