Help me solidify my decision on a "normal" prime for a 40D.

[In2Photos]

As some of you already know my wife and I are expecting our second child around Halloween. I have also been doing more and more team and individual portraits for a local youth sports league. I have been using my 17-70, stopped down to f/5.6, for the T&I shots and have prefered the shots taken around the 50mm mark for individual shots, and around 25-30mm for team shots. This seems to give me decent background blur, but I want more. The 85 is too long for either shot and the 50 would be too long for team shots. So this got me thinking that I need something wider, perhaps in the 28-35 range to use for all shots.

Now I also want to make sure I can use this lens for low light, non-flash stuff when the baby comes as well as having something wider to use with flash for indoor as well.

The lenses in this range are:

Canon 28 f/1.8
Canon 35 f/2
Canon 35 L
Sigma 28 f/1.8
Sigma 30 f/1.4

Now the L would be nice but too expensive so it is out. I think the 35 f/2 would be OK but I would really like USM/HSM for when I need to catch the kiddos running around. The Sigma 28 doesn't seem to have much of a following here based on the archive. So that leaves the Canon 28 vs the Sigma 30 (have we seen this before?)

Both archives have lots of great pics, but the Sigma seems to be the leader. It is a DC lens, but I already have one DC lens so that doesn't bother me (I could sell both my Sigma 17-70 and the 30 for a 17-40 or something and another prime).

Any opinions on either lens would be greatly appreciated.