friendly with the Jedi and the cause of restoring the Republic, so there was no reason not to let them raise Leia, and every reason in the world to entrust them with Leia's upbringing.  
Leia was relatively safe with the Organas because they were very high-profile people, royalty in fact, and even the Emperor was wary of the negative publicity that would result from any attempt to kill the ruling monarchs of an important planetary system (at least until he had an operational Death Star which made it less important to maintain popular support).  In a way, the visibility of the Organas made it possible for the remaining Jedi to keep an eye on Leia from afar.
Owen Lars was a simple man living in a remotearea on a desert planet in the middle of nowhere.  He was very low profile and not visible at all.  That meant that someone would have to stay close by in order to keep an eye on Luke.  Obi Wan volunteered for the job, presumably because of a combination of factors- his close relationship with Padme and Anakin, the guilt he felt for the way Anakin went astray under his tutelage, the fact that he (presumably) thought he had killed Anakin, and on a more practical level, because he had very little else to do with the rest of his life.
I never got the impression that Obi Wan didn't care about Leia, or cared more about Luke - it was a pragmatic decision, as I