First of all, yes, the lens mount is the same on all EOS models, so all lenses fit all cameras.
I have the 28-135mm lens on my EOS30, which I use for most of my general photography. I have a 70-200 and a 170-500 for aviation.
For the F2.8
The 28-105 should be better, being f2.8-4. Generally, an f2.8 lens used at f3.8 should be sharper than an f3.8 used at f3.8 since it is stopped down.
You also get the oppoptunity to shoot at F2.8 in low light.
F2.8 glass tends to be better.
The extra length from 105 to 135 is probably covered by your other longer lens.
For the F3.8
Lighter than an F2.8
Cheaper than an F2.8
Good 1:2 macro if you want it
Have a look at the reviews here.
This was taken with the 28-135.