I finished S1 (US) around a week ago and decided to get the British version and the similarity between the2, plot-wise, is very high. So I am hesitant to watch s2 (UK) since it will probably spoil S2 (US).
The characters between the 2 series are essentially identical. I prefer the UK Frank. Macey's acting is great as the US Frank but the writing for the US Frank is just less believable.
I do prefer the US Philip, he is a very interesting character for sure. It seems like the US series started focusing on him more as the Season progressed.