I have had the best luck with wet cat food: orange or red can fancy feast or purple can meow mix. In live traps, I put about a quarter can or less into a peanut butter jar lid (3" diameter, half inch to 3/4" lip). Drop it into the trap and slide it to the back, lets you avoid rubbing your scent all over reaching into the trap. In trap sets, I put a 'glob' about a quarter the size of a golf ball or a bit less on a gatorade lid to keep the bait up off of the ground in a shallow hole set right off of their trail.
When I place live sets, some of the most productive spots for me have been placing the trap under bridges and culverts where coons have walked down a hard packed path along the sides. Set the trap in the path along the wall so they would have to walk through it, or refuse the bait to walk around it.
Sardines just haven't produced for me.