The answer to this question is a completely subjective one. What this means is that the answer is based upon the reader's (my) personal thoughts about each of the characters. This being said, there would surly be alternative views based upon how one feels in regards to each of the characters in question.
Grover dies in the first section of the story. Some may feel connected to him based simply upon the fact that his life has been cut short. Others may not have had time to find out enough about Grover to connect.
Eugene, the narrative voice in the final section, is the one with whom many may find a deeper connection. Given the fat that until returning to the home in St. Louis to remember his brother, he has forgotten him. It takes Eugene's return to the home for his physical senses to fully recreate a memory of his brother.
Therefore, many may relate to Eugene (declaring him to be the "better character") based upon the fact that they too have been reminded of a far lost memory based upon smells, sights, and sounds.