I don't think there's a MD 28-70mm with constant 3.5 aperture.
There's a MD 28-70mm f3.5-4.8 (not Rokkor, no macro mode), there's also a 28-85mm f3.5-4.5 (with macro mode).
Quite a few of us here like the 35-70mm f3.5 with macro mode. Look in "Sample Image Archive", or do a search.
Rokkor is just Minolta's branding. Like Nikkor for Nikon, Hexanon for Konica.
Which one you pick depend on your preference. Do you value zoom range for convenience, or constant slightly faster aperture with macro mode? The 35-70mm got very good reputation. Personally I'd pair it with a 24mm or 28mm.
I have never been a fan of manual focus zooms on the NEX...until now. I picked up a Rokkor MD 35-70/3.5 macro and I love it. It has wonderful sharpness and between 35-50 is it approaches prime lens level of sharpness. The macro part makes it a very flexible lens. The MFD is .8 meters otherwise. The front element rotates when focusing so if you use circular polarizers it may not suit you. It is reputed to be the same lens as the Leitz 35-70R Vario-Elmar. I find that it has a nice balance of sharpness, rendering, color and bokeh. It is a bit less contrasty than some lenses but the results are very pleasing. It makes a very nice lens for a lot of situations. The lens extends to go wide and comes in for zoom which took some getting used to but it has quickly become my favorite walk around lens.
The other Rokkor zoom lens that I would look at is the Rokkor MD 24-50/4. It is supposed to be a bit sharper in the center than the Rokkor 24/2.8 and softer in the corners. It's about double the price of the 35-70 but from everything I have read it is a very VERY nice lens.
Here are some samples of what the 35-70/3.5 macro can do on the 5n.