Wide range lens for Sony nex-c3 with adapter?
I am looking for a good wide range lens for my sony nex3. I currently only have the lens kit 18-55 and am badly needing a zoom lens. In the somewhat near future I am going to be purchasing a SLR and am leaning towards the canon t4i, so I want to get a lens that will be able to work on both cameras. Although I have read that there is a certain adapter that I need to get in order to not lose the AF for the nex. I was looking at third party lenses because of cost, but I have no idea where to start because I have never bought a lens before. The only one that I have read about is the sigma 18-250. Is this a good lens or is there something better out there? Is it way better to save for a canon? And if so, which one and what is average cost? Although, I would prefer to go the cheaper route as long as the lens is good. Is Tamron better than Sigma? Just don't know where to start. I would be photographing a wide range of things such as family, vacations, portraits, sports (my son's), etc., but don't want to have to change lenses all the time.
Please help with the best all around lens for wide range