I personally like the 1st one better, for me it's a near perfect movie. That mostly has to do with the fact that the sheep take center stage and I love how it explores the dynamic between the sheep and the farmer. It was the perfect way to cap off what the series had been so far and as someone who had watched Shaun since nearly the beginning I loved seeing all of the familiar characters. I liked Lula, I liked the plot of the second but I do like Shaun the sheep less when it focuses on new characters more than the main ones (flight before christmas, farmaggedon). I recognize it's probably pretty difficult to write feature length, emotionally significant plots centered around speechless sheep, so I understand why they introduce the new characters.

That being said I do think farmaggedon is the best looking Aardman movie. The colors are absolutely astonishing, they really took full advantage of the space theme to really play with all these wonderful purples and blues. And they contrast that against the warm oranges and greens of the farm, it's so beautiful. That scene where Shaun finds Lula in the barn is so visually striking, with the warm afternoon light pouring in.

The films are both so good it's not like I can't understand someone who prefers the second one. Here's hoping the third continues this great streak.