With the availability of so many wonderful classic Minolta lenses, it can be hard to decide on what to get. In my case, I just got them all (almost) and that made the decision a lot easier!
Light gathering. Same. f3.5, f4, f4.5... we wont see much of a practical difference. Neither have the convenience or "neat" factor of a constant aperture either.
Focusing - advantage 28-135 (faster). In my experience, the 28-125 is faster and more accurate. The forums seem to general agree with that assessment as well. The focus mechanism is different on each. The 35-105 has the traditional screw drive with a front focus ring. The 28-135 has a rear placed focus ring - still screw drive of course but a different design. It feels and sounds like the 28-135 is moving fewer parts of less mass. It is also a bit quieter than the 35-105 but neither will win any awards as far as that goes.
Image quality - advantage 28-135. Concerning sharpness, subjectively, they are roughly the same. However, the 28-135 has that certain something special to its images. While most old Minolta lenses have decent color, sharpness and out-of-focus areas, the 28-135 takes it all a notch above.
Build quality - same. Classic Minolta, you can't go wrong - metal body, metal mount, smooth operation. I have read some forum posts that stated the 28-135 is more fragile, but information about this is far too anecdotal to say for sure.
Bottom line - it depends. While certainly the focal length range of the 28-135, fast focusing and beautiful image quality make the 28-135 a lens to love - it is bigger, heavier and more expensive. The 35-105 is still a great choice if the limiting focal-length range isn't a show-stopped for you.
I didn't mention or consider the 28-135's macro mode since most find it more of a feature to forget than an advantage. The macro is usable but (being generous) of limited usefulness.
My opinion? 28-135mm, no question! The image quality sets it apart and fantastic range make it a real winner for outdoor shooting. Indoors f4-4.5 is somewhat limiting and combined with the 28mm (42mm on APS) wide-end makes less than ideal. Indoors I prefer the Tamron 17-50/2.8.