large aperture standard zoom lenses - get Tamron

Canon EF 17-40mm F4L, EF-S 17-85mm IS, EF-S 18-55mm, Sigma DC 18-50mm F2.8 EX, Tamron AF 17-35mm F2.8-4 Di comparison

get Tamron 28-75mm
Canon EF 24-70mm f/2.8L USM 83.2x123.5mm, 950g, 77mm, 0.29x, 38cm, $1,133
Tamron Lenses: SP AF28-75MM F/2.8 XR Di Tamron vs. Canon 73x92mm, 510g, 67mm, 0.26x, 33cm, $349
Sigma 24-70mm F2.8 EX DG MACRO Sigma 24-70 f2.8 vs Tamron 28-75 f2.8 88.6x115.5mm, 715g, 82mm, 0.29x, 40cm, $383
Tokina AT-X 287 AF PRO SV 28-70mm f/2.8 84x108mm, 719g, 77mm, 0.2x, 40cm, $259

Canon 17-55mm > Sigma 18-50mm > Tamron

Canon EF-S 17-85MM f4-5.6 IS USM 78.5x92mm, 475g, 67mm, 0.2x, 35cm, $499
Canon EF 17-40mm f/4L USM 83.5x96.8mm, 475g, 77mm, 0.24x, 28cm, $665
Canon EF 28-135mm f/3.5-5.6 IS USM 78.4x96.8mm, 540g, 72mm, 0.19x, 50cm, $418
Canon EF 16-35mm f/2.8L USM 83.5x103mm, 600g, 77mm, 0.22x, 28cm, $1304
Canon EF 24-105mm f/4L IS USM 83.5x107mm, 670g, 77mm, 45cm, $1193
Canon EF-S 17-55 f/2.8 IS USM 83.5x110.6mm, 645g, 77mm, 0.17x, 35cm, $1180
Canon EF 24-70mm f/2.8L USM 83.2x123.5mm, 950g, 77mm, 0.29x, 38cm, $1129

Nikon USA: 17-55mm f/2.8G ED-IF AF-S DX Zoom-Nikkor 85.5x110.5mm, 755g, 77mm, 0.2x, 36cm, $1156
Sigma 18-50mm F2.8 EX DC Photozone Test Report / Review Photo Gallery by joe at pbase.com Comparison with Canon 17-40mm, 24-70mm 74.1x84.1mm, 445g, 67mm, 0.2x, 28cm, $408
Tamron 17-50mm Di Lens - PhotographyBLOG Tamron SP AF 17-50mm F2.8 XR Di ll LD Aspherical (IF) 74.0x81.7mm, 434g, 67mm, 0.22x, 27cm