Haven't read the whole thread yet, but what I do love about both of them is that--like Kirani James and LeShawn Merritt--they go out there week after week to race each other. Great pair of rivals. Their differing personalities (from the little that we know about them...we don't have the press following them around and writing articles about them incessantly like other professional athletes in other sports) only add to the drama.
I used to be a Jenny Simpson fan to the detriment of Shannon. I definitely liked Jenny more, and didn't particularly like Shannon. But the more I follow Shannon and keep watching her after the last few years, the more I like her. I know everyone likes to make fun of her for the lipstick, but it seems like a sweet reason for wearing it. Plus she ran...3:56? Either that or 3:57. The AR was pretty sick and by a convicted doper, and everyone assumed that Simpson would get it (and I still want her to), but Rowbury went out there and bagged it.
I do think that Simpson has had the slightly stronger career thus far, but their careers ain't over. Are they around the same age as Webb and Ritz? I wish that there were more interesting personalities that are up in the mix in the top Diamond League races on the men's side in the US. There's been Centro the last few years, but that's about it. Although tons of US guys came out of the woodwork this past year (Berian, Clayton Murphy, some others). I hadn't even heard of Clayton Murphy really till the Olympics! But Jenny and Shannon have been out there year after year, running with the very best. Maybe not always winning, but they certainly push each other to heights that neither of them would reach without the other one prodding them.