It may seem obvious, but you pay for what you get. 😉 There’s a reason why Sigma lenses are cheaper than Canon/Nikon lenses…

There are loads of reviews, comparing them both on the net though.

Hope these are useful:
http://photography-on-the.net/forum/showthread.php?t=57174

http://www.outdoorphoto.co.za/forum/showthread.php?t=760

Cheers,

Alex
http://alexpeake.fotopic.net/

I current use a Canon 350D with a 18-200mm (Tamron) & 100-400mm (Canon IS) lenses and find they suit nearly all situations.

The 18-200 will suit anything from landscape photography, to portrait photography. I imagine it’ll cover most needs for family stuff to.

I can 100% recommend the 100-400mm IS Canon lens though. Yes it’s bulky and heavy, but the image quality is suburb. Even on a 350D the quality is outstanding. Just goes to show that good quality glass and IS really improve results. You can get some cool panning shots to, as the IS will allow a slower shutter speed for you to pan with, keeping the subject sharp. EG:
http://alexpeake.fotopic.net/p33659581.html

I’m mainly an aviation photographer and have set up a website. Please feel free to check it out at this address: http://alexpeake.fotopic.net/