Be prepared for my long rant:
Harry&Ginny: Okay, so first I'd like to say that I do not believe Ginny even deserves Harry. She's undevolped. But I won't get into that too much. I don't think they belong together because:
-It was random
-They are not 'perfect' for each other because they haven't been there for each other
-She's a fangirl and used guys that Harry knew so he'd like her
My first point: Harry didn't care at all about what she did in book five. She was going out with Dean and Ron got mad, but Harry thought he was over-reacting. In book 6, however, he has a monster in his chest! Many supporters of this ship say because they spent time together. They spent probably TWO MONTHS together in summer. Sure, u could devolp a crush, but getting married after barely noticing them? The 'monster' in his chest was random and was no better than the 'whole' in Bella's chest in Twilight.
Before Harry liked her, they didn't even go through the same experiences. Yes, they fought at the DOM, but she wasn't there fully nor did she even know what was going on. Before this battle, she was always a tag along and she wasn't there for him when: he was going through the stress of the Triwizard Tournament, understanding Peter's betrayal, dealing with the dementors. Ginny was at school when this was going on, but why was she not involved? Many people say Harry and Ginny have a lot in common, but I'm sure that Harry would never tell her his worried about Voldemort. Not because he cares about her, but because he would feel that she can't understand it.
Also, Ginny had a crush before she got to know Harry. Why? Because, silly, he was the boy-who-lived. She was in love with his titel before even getting to know him. Than, in book six, she zei Hermione told her to act normal around him and she thought that door going out with other people, he'd notice her. That's probably why she didn't feel bad dumping her boyfriends. She was done with them: they had played their parts. I could go into a longer, much meer detailed debate, but I think this should do.
Now, Hermione and Ron:
Ron has always acted like a prat and has been careless with her feelings. So many times he made fun of her and hurt her. Every time he did, instead of acting like mature adults of people, they didn't talk to each other for weeks and weeks until Harry got sick of it and told them how stupid they were acting. Just imagine, if they could fight and not talk for that long, what would happen if they got in a fight when they were married? Probably divorce. So many people say that this constant bickering shows how much they love each other, but really, in reality, they would probably not be vrienden in the first place. In fact, I think if Harry hadn't been there, they would stil despise each other. Their personalities are differant too. While Hermione is smart and logical, Ron jokes a lot and doesn't pay much attention to education. It just doesn't make sense. Even J.K Rowling zei that Hermione was based off of her. She zei she married a Ron at first, discovered it could not work, and now is happily married with a Harry. That should pretty much sum it up.
Sorry for this answer being so long, but I feel strongly about this =]