I think I'm the only one who loves Let's Kill Hitler, and doesn't get the dislike it sometimes gets. Then again, I also loved A Good Man Goes to War, and I think River is awesome, so I'm not unbiased.
That said, Season 6 is mixed. I loved the River stuff, there are a bunch of generally great episodes and A Christmas Carol (which I guess technically counts as Series 6) is one of my favorite episodes of Doctor Who. But, even though I kind of like the episodes they're in, The Silence is my most hated bad guys in Doctor Who, period. More than even the Slitheen, I wish the Silence never existed. So, the fact that they're basically the big bad guys of Series 6 drags it down a bit, otherwise it would probably be my favorite Series of NuWho. As it is, its up there, but I honestly have a hard time choosing a favorite Series.