Upload & Sell: Off
Here are my preferences for mid-range alt zooms:
1. Contax 35-70/3.4 (still have)
2. Leica 35-70/4 (sold)
3. Olympus 35-80/2.8 (still have)
4. Contax N 24-85/3.5-4.5 (still have)
The Contax N is nice because it's auto-focus. Optically, I've never been that impressed with my copy or other sample pics I've seen on FM. Many will say it's a great lens, but it's just never wowed me like the manual focus Contax lenses have.
The Olympus 35-80/2.8 is attractive because of the constant 2.8 aperture, which allows for a bit more creativity with DOF, and most importantly, it produces very nice results compared to almost all other Olympus lenses. Unlike the trademark understated colours of other OM lenses, the colours of the 35-80/2.8 are more saturated. And it's plenty sharp. You won't want for sharpness with this lens. Ergonomics are fine if a bit odd due to the ball-bearing focus ring. The zoom ring is too narrow, in my opinion; zooming isn't nearly as buttery smooth as, say, Leica. Not even close.
I also have the Olympus 90/2, and like Paul, I would take it over the 35-80/2.8 if I could have just one. But the 90/2 does suffer mildly to moderately from CA and fringing (? - sorry don't know the correct terminology here) if you're not careful with it. But it's sharper, and the colours are "better" in my books.