well i see that this discussion already is a bit old..
but i have the similar problem..
i already bought the sigma 70-300 APO DG Macro, and i really like how it's behaving in its focal lengths, but. since it's the only lens that i have, i miss, smaller focal lenght, since sigma starts from 70mm and it's quite far already..
i updated with my shots the review of Melvin's full amateur review of the lens performance in this thread:
after I bought this lens and after a few days of extazy, of using it, i started looking, how to get wider angle.. and noticed, that sigma has that.. 28-300mm DG macro.. well then I started to go mad..
should i sell my current? will the new one, will be as good as the current in telephoto, macro, and overall image quality..?
did not find any reviews or comparisons..
finally, decided to keep, this 70-300mm, since i have good overall quality of images, good telephoto, quality, better macro, than 28-300mm would give. so with 70-300 i solve telephoto and macro desires satisfactory
however Landscapes, and portraits are not satisfied.. and i will not likely would want to change lenses every minute.. so i need something versatile.. with wide angle and portraits capability and some telephoto abilities..
So now, i'm looking at tamron 18-250mm
because, changing lenses.. is so annoying.. unless you decide, i'll be shooting mainly telephoto; macro. otherwise you want some landscaping, some portraits, some moderate telephoto..
anyone else is solving similar issues?
what are your solutions?
by the way I also have a small budget.. so, all becomes even trickier..