I have a gas stove and I'm insalling a Range vent hood. The handiman who is installing the hood is adding a flexible vent through the roof. Is the roof the best or only exit for the range?

I read that is it best not to use flexible ventilation but to use metal. Does it really make a difference? Is there some other material that i can use that is in between.

I'm also venting my bathrooms. I'm thinking about venting them through the soffits. I hear that i should limit my roof penetrations. Except for the vent fan which pushes the air out, i don't see my moist air would run through the soffits since hot air naturally rises.