med. blue fluorescence is not going to have a big impact on color. in the two examples you posted, the percieved difference would largely depend on the viewer as well as the lighting conditions. one will not look substantially whiter than the other in either case.
Both stones are from an internet vendor so it would be difficult to compare them.
I always thought I was okay with an I stone but I had a different vendor send what I thought was "the one" to an appraiser so I could take a look and it really faced up yellow. Not sure if it was just that stone or the fact that this was the first one I saw outside of a jewelry store setting with the fancy lights.
Are the stones at the same internet vendor?
is it someone you can call and ask them to look at both and give you an honest opinion?
Personally - and this is VERY personally, I wouldn''t buy an emerald cut diamond in an H or an I, because I can see the color - and I don''t like that look. Not everyone will agree with this point of view!
But - if the vendor can give you and honest opinion, or even send both stones to a local appraiser for you to see, then you won''t have to guess!
I agree with Forbidden- I can see color very easily, and personally, I wouldnt go under a G with an EC....it is very easy to see color in the EC''s compared to other shapes...
To answer your question, it is hard because there is no clear-cut answer to that. I would have to see both stones together to make a decision. You have to see the cut of both stones, which is the most important, even more important than color...