Here's a food thought, I think what affects people's thinking that Sangakkara is not as good as some of the other ATG batsmen is that a lot of his most talked about knocks has come in games where other batmen (either from his own team, or opposition, or both) has also managed to put up big scores, Whether it be the 192 vs. Australia, 147 vs. England, or even recently 203 vs. New Zealand and etc.
Even his world cup success recently, which enhanced his reputation a whole lot more, follows this trend somewhat.
Now in a career that's spanned so long he has probably done the vice-versa as well, and other ATG has probably done what I'm describing above a fair bit as well. But I have a feeling it's happened quite a bit more in Sangakkra's case. I'm too lazy to look this up and confirm if I'm right or wrong in this at the moment, but definitely thought it was a worthwhile discussion to throw out there.