The Harry Potter Books are a masterpiece of cohesion and symbolisms which keep recurring. Just think of the goose-pimple evoking symbolism of mothers saving their sons and, hence, saving the world and Harry. Lily sacrificed herself for her child and Narcissa saved Harry once more because she wanted to see her son, Draco. It is genius.
There are also many opinions on the similarities between Harry and Tom Riddle, alias Lord Voldemort: they are both orphans, for both Hogwarts was their rescue, they are both talented wizards and are very determined. Still, I think there are bigger differences between them than similarities after all but let's have a closer look.
True, Harry and Tom are both orphans and grew up in a less than loving environment; still, Harry had a few big advantages in his early stages of life. First of all, Harry shared his first year in life with his doting parents whereas Tom was given to the orphanage by his mother shortly after she had given birth. Neuroscientists claim that many connections in the brain made are already joined in the first year and determine greatly how the brain will develop. Harry's one-year-old brain was fed with love and warmth whereas Tom's start into life was rocky from the first breath.
Secondly, consider under which circumstances their parents died. Harry's parents loved him so much, they both (yes, let's give James some credit, too) sacrificed themselves for him; James to help Lily escape with Harry and Lily, who died for her son. Tom's father, on the other hand, abandoned him and his mother before he was even born and his mother couldn't even stay alive for him and fight, but rather gave him and herself up. Of course, this is all circumstantial, but it is arguable that knowing under which circumstances your parents gave you up or died matter greatly to your further course of life and how you perceive it.
Thirdly, they both grew up under less than loving circumstances. Harry had to endure the permanent picking of the Dursleys whereas Tom suffered in the orphanage. I don't know if you are familiar with JK Rowling's charity Lumos, but it actually aims to get children out of orphanages and into families - even if they're foster families. Despite Harry's unfortunate situation with the Dursleys, he was still part of a family system in some way which - as far off as the Dursleys sometimes made it for him - was still some sort of home. Tom's early upbringing in an orphanage ensured he never knew what having a family was like and it benefited his development into an emotionally and socially repressed person. From very early on, he had to look out for himself and empathy, as some experts suggest, is something learnt in early stages of childhood and is hardly re-learnt once out of the right phase.
Many people would probably claim the biggest difference between Harry and Tom is that Harry was in Gryffindor and Tom in Slytherin, and I agree to some extent. However, as stated by many it was a mere lucky coincidence, I don't believe it is about luck, but about a conscious decision. Dumbledore once rightfully said that who we are does not depend on our character traits, but our decisions. Harry chose to be in Gryffindor because what he was seeking was a sense of family and community and he knew he would have a better shot at finding this in a house such as Gryffindor. Tom, seeking followers rather than friends, chose Slytherin because he knew he would find them there easier and his emotional detachment would not stick out as obviously in Slytherin as in other houses, perhaps. This proves that even before they came to Hogwarts, Harry and Tom were fundamentally different in their way of thinking and their wishes for their future lives. Tom was already seeking power over other people whereas Harry, a far more insecure and vulnerable soul at that point, chose true friendship.
One of the greatest things I think about Harry is that, not even once, he considers killing someone for real. Harry never uses the Death Curse, not even in dire situations. Just think back when they fly him to the Burrow in Deathly Hallows and instead of killing the Imperiused Stan Shunpike, he merely disarms him. Harry is the gentlest and purest soul without losing his humanity, which makes him a true hero. He is not perfect, but he is truly good, which makes him as distinguishable from Tom Riddle as it could possibly be. The books show very well that even if two people start out quite similarly, they can always choose to be good, regardless how they have been treated in life.