I said the diagonals were horrible because there is a diagonal bias making the diagonals too easy to accidentally hit. This is not an issue on some games but it makes a lot of games unplayable IMHO.
The screen is a matter of preference. After having owned both the mk1 and now I have the mk2 I think the mk2 screen is much better without as much flicker. Also while the scan lines of the mk1 kinda look more authentic, I think the mk2 screen looks a lot better. Also my mk1 had a vertical line visible on solid colored screens. As for the viewing angle reduction of the mk2 it's just a matter of holding the system at the best angle. Anyway have fun and play whatever you like and or want to buy or not.