The 35-70mm f3.5-f4.5 is considered a very good lens, and hardly any bigger than the 50mm f1.8 prime. I have been using a 35-70mm f3.6, but it is big and heavy, and ruins the balance of the camera. So recently that one has been left at home.
I have begun to think just carrying a 40mm or 50mm prime is the better overall choice. You can typically move back and forth a few steps to get the proper composition.
Olympus 35-70 f3.6 - superb two-touch lens with fixed aperture. Rare and sought-after.
Olympus 35-105 f3.5-4.5 - high quality one-touch zoom, going for peanuts on the 'bay these days.
Olympus 35-70 f3.5-4.5 - tiny two-touch zoom, suprisingly sharp a little too much barrel distortion at the wide end for me but a terrific travel lens (weight & size match 50mm primes). Don't confuse it with the inferior Cosina-made f3.5-4.8.