Why doesn't Pedro, Villa, Neymar etc. score like Messi? A fair share of his goals are through his individual quality. Good players benefeit form playing with good players, you can't knock Mess for that. He would be the best player in the world even if he scored half the goals he does, no player can change the game the way Messi can. He has been carrying Barca the last season or so too, he is the main reason they won La Liga and reached the Champions League semi-final last year. Uruguay have a much more balanced team than Argentina do, sad but unfortunately true. Argentina are also improving as a team, Messi is a big reason for that. He plays a different role for them, he is not needed to score but to create and control the game in the oppositions final third. So looking at their international goal record is somewhat lazy.
Messi has scored against and impressed in the biggest of games and has done so consistently something Suarez does not have on his cv. He doesn't have the teammates to put him in a position to shine in the bigger games you may argue, so if/when he eventually moves we will get to judge them better.
Messi is on a different level to Suarez.