They both were as you say in the same boat. They were orphans who found a home at Hogwart. Both has bad upbringings.

I asked about DIFFERENCES

the difference, harry got lucky for having a TRUE friends and good memory of his parents. a little light in the darkness some would say

Just like FleetingFacy said, plus Harry had been the centre of everyone's attention whereas Tom must have been a "nobody", at least in the first year.

of course, they were just that much alike because Harry had literally a part of him inside, the had diferent interest in likes and dislikes, their families were diferent.

1) Harry never got to live in an orphanage.
2) Harry had wealthy parents who provided for him
3) Harry had the most powerful wizard looking out for him.
4) Harry was famous throughout the wizarding world.
5) Tom's muggle parent rejected him while Harry's muggleborn mother died protecting him.

Tom grew up in an Orphanage during the Depression and World War II. I don't really think that their childhoods are comparable. If you don't understand my reasoning just look it up in wikia.