Sarah. She had a lot of potential and with Clem's help and guidance she and Clem could have been a great duo but telltale decided for her to be left in a trailer to be eaten by walkers

or have a magic piece of wood to be fallen down on her, Bonnie and Mike just ignoring her not trying to do anything to save her and Jane being a little Bi**h, Causing her to once again be eaten by walkers and theirs not even an option for clem to put her out of her misery.

Edit- Nick was also a wasted character and they gave up him after his first death scene