I'm suggesting a couple of things. For one, its important to know that the grading is accurate. For me, I feel pretty confident in the accuracy of a report if its from GIA or AGS. That doesn't mean other labs don't grade accurately, but from my experience as a consumer and researching as much as possible before my purchase, other labs may not be as consistent in their grading. This is especially important if you are purchasing online and aren't viewing the stone in person.
My point about color is that for "most" people, once a stone is mounted a G/H color should really "face up" as colorless. Certainly their are some people that have better color acuity than others and may be able to tell that an "H" color has some tint when loose, but I think once its mounted, its much more difficult to tell. If your goal is to have a diamond that appears colorless when mounted, I don't think you'll go wrong with an H. Obviously its important for you to do your own color comparisons to see if you can tell the difference. Keep in mind that diamonds are graded for color "table" down by viewing through the pavilion. So, if you put a "D" colored diamond next to an "H" colored diamond in a white tray, table down next to each other, you will most likely see a difference. However, again, your diamond isn't viewed that way in real life. I don't want to influence you to an "H" color, I just want to make sure you understand how it looks and keep your options open. It all depends on your budget and what is important to you.
As for clarity, again it depends on what you are looking for. Do you want a diamond that is "eye-clean"? Is it important that if you view the diamond through a loupe that you can't see many, if any inclusions? My point about SI-2 is that again, who graded it is important. If it is truly an SI-2, you may not notice any inclusions with the naked eye. However, that grading is "on the border" such that some SI-2's may be eye-clean and some may not (even if properly graded). So, if "eye-clean" is important to you, youmay want to narrow your search up to SI-1/VS-2.
Bottom line as I stated above is that its all about what's important to you. For some, size is #1, others want a colorless "D" diamond and will sacrifice clarity, others want a diamond with no inclusions visible, even with a loupe and some choose to concede a little in all three areas.
Sorry for such a long post, but there is so much to say and think about. Good luck!
E