Justin,
I own both the 17-40mm Canon and the Sigma 70-200mm. I can't comment on the other two lenses.

The 17-40 is my basic working lens and I love it. The F4 is not a problem since I can gain back that stop by shooting at ISO 200 rather than 100. Most of the time I'm shooting this lens at F8 and it's pretty sharp.

The 70-200 F2.8 is very sharp and it has been my long-range workhorse. At 70, you get a nice portrait lens. At 200 on my 1.6 crop-factor XT, you get a pretty nice long telephoto and the Sigma 1.4X teleconverter works with this lens for a nice long reach. Again, this lens is sharp.

For an additional $70, I'd recommend the Canon 50mm F1.8. It's incredibly inexpensive and very sharp especially stopped down to F8 or F11. In my opinion, it's a "must have" for every Canon shooter. A great portrait lens.

Those are my comments. If you have any additional questions, just yell.

Jim