Naruto's story is really sad, but...

1. Gaara was lonely for a lot longer than Naruto.
2. Gaara's father tried to assassinate him.
3. Gaara accidentally killed his uncle, the only one alive who seemed to care about him, only to be told his uncle actually hated him and his mother had hated him. I believe that Gaara's mother's love was Gaara's 'sun' as a jinchuuriki, which is why Shukaku took over him at that point.
4. Some of Naruto's classmates (e.g. Shikamaru and Choji) weren't actually THAT unfriendly towards him, whereas all the sand villagers really hated Gaara, some going so far as to tell him to go away and die. :(
5. Gaara was never able to sleep until Shukaku was extracted from him. EVER. Oh, apart from that one time when he was fighting Naruto.

So yeah, I personally think Gaara suffered a lot more than Naruto in his childhood, though I'm not saying Naruto didn't also suffer a great deal, of course.