Rationale for wide prime lenses
When it comes to lenses that are compatible with both crop and FF cameras, if one left out the L lenses (24L, 35L), what would be some reasons to consider the other primes (like the Sigma 20, 24 1.8, Canon 20/24 2.8, Canon 28 1.8, 35 f2)? The two Sigmas mentioned are not favorably reviewed. The 20/24 Canons are said to be soft wide open. So if you have to shoot at smaller apertures then doesn't it make sense to go with the 17-40L or the 24-70L or the Tamron 17-35? The only decent ones in this list appear to be Canon 28 1.8 and the 35 f2, and neither is really wide.
The zoom, too, have their cons. The 17-40L is simply not fast enough. The 24-70 is expensive and heavy. I've read mixed reviews about the Tamron.
So, what does one do to get a wide lens (prime or zoom) that's faster than 2.8, and has decent IQ? Fork out the money and get the 24L or the 16-35L, I suppose.
Rebel XT, Canon 100 f2, Canon 100-400 IS, Canon 50 1.8, Sigma 18-200 OS, kit lens