Matt Smith at a recent Wizard World Comic Con was asked what his best and favorite series was. I'm not surprised by the answer and in fact I have to agree with him as the series he picked was my favorite of his also. Here is his answer and what he thought about it all.
"For me, the best storytelling was in series five. It had great adventure and great clarity, and I loved the whole idea about the Pandorica and the Big Bang. It was the one I connected with most. Looking back, I think some of my best work was in my first series, because I was actually taking real risks and that was a real moment"
Then he was asked what his best speech was during his tenure. "I think it has to be when I was talking to the spaceships in The Pandorica Opens"
Then he commented on the big reveal in Series 6 about River being Rory and Amy's daughter. "I think in terms of revelations, River being Amy's daughter was a bit 'what the hell!'"
Source: Den of Geek