DurhamRookie, As you know, Sony has been a good producer of electronics for decades, but did not rise into the still camera and DSLR world until the digital age. My only experience with Sony optics is from their early and pioneering portable video cameras in the 1970's, but those lenses are no comparison to today's optics for DSLR's. I do, however, have experience with Sigma lenses and I have a couple of f/2.8's that I use with my Nikons which render excellent results. My gut feeling about your choice would be go for the proven experience, go Sigma.

Apparently you are unaware that Sony bought out all of Minolta's photography business, including camera and optics. In addition Sony has also had relationships with a number of lens producers in addition to the complete Minolta line, like Zeiss.

In other words Sony is using and adding to where Minolta was with both cameras and lenses a few years ago, plus adding their own R&D capability to what they are offering.

So, just because you aren't aware of a brand name's entire history, is it a reason and justification to discount it?

Sony used to be a lot better, but these days I would go with Sigma

I have both the a100 and a700. I'd go with the sigma 70-300. I have that lens and use it on my A100, as my standard len. I also have the sigma 18-125 which I use as my standard walk around lens on the a700.