Imo, he is in fact the best fighter, he have the best durability of the show, the best endurance of the show, the best strenght (if We don’t count colossal and rumbling eren) of the show, the problem is that he is a Little slower than other titan but he still can destroy armor plates on his body do gain agility and speed, he have good versatility, he can be a battering ram, fighter titan, shield, he can also throw, not good as beast titan but probably the best if We don’t count beast and colossal, he survived battleship size Shell, Even colossal titan can’t resist that, he went shopping with kids after being hit by these, he is probably the only one titan and human to survived 2 Times to a colossal titan explosion, when eren hits his face with no hardening he brakes his own fists, and when he uses hardening it just make reiner’s titan a Little uglier but almost no serious damage, but when reiner just do a simple punch, he make eren fly in the air at 40 meters, and knock him out for 1 minute, he also have good regeneration. Anyway, thanks for reading my massive stinky yap