I would much rather have Hayden and Sehwag than any other, and I don't buy this 'partnership' crap. You pick your best batsmen, and the comfort level comes from playing with each other over a period of time. Most of the elite players have many century partnerships with almost everyone else in the team, so I don't buy that you have to pair them up just the right way.
Second, I don't see an issue with two players seen as super aggressive. First, Hayden was dominant, but he wasn't super aggressive in terms of his strike rate. He had an above average S/R, but his S/R is similar to Pontings or Lara, for example (though obviously neither was an opener, which helps). Sehwag's S/R is off the charts, especially for an opener. Langer is only 6 S/R behind Hayden. Sehwag is 20 ahead of Hayden.
Third, the idea that you want one to 'stick around' and the other can be hit and miss is flawed in two ways. First, that it's actually true that Sehwag or Hayden are somehow more hit and miss than Langer. Look at the number of matches played vs. number of 50+ scores. They all get to 50+ pretty often, and actually at close to similar rates. Second, the fact is when they both hit, you've virtually guaranteed yourself an awesome first or second innings score/chase, or at least a very good start. And that is priceless for the middle order.
So my point is, people should pick the two best batsmen (whoever you think that might be), and not worry about how they may or may not fit together out in the middle, or to look at their styles too closely. As selectors, you would generally pick the next best batsman if an opening is available, and I think people should do the same thing here.
Obviously, it's fair enough to pick Smith or Langer or whoever, as they are both successful, and I could have picked either as well, but it should be because you think out of the three, individually, that the batsman is the best. I think Hayden is a shoe-in though as the best opener of the decade, but I don't think he is as far ahead of the others as perhaps some think.