The up side: They are reuseable. They do last a long time. They force you to change the baby more often, which is better for the baby. Kids will often toilet train easier because the diaper is not comfortable, while the disposables keep moisture away from the baby. It keeps all those diapers out of the landfill. And really, have you ever seen the goop that is inside a diaper??? No, I don't mean the baby's mess, I mean the gel that the diapers are made of---scary. I saw a disgarded diaper that had broke open and that gel was disgusting---it looks like a hazardous material to me.
The down side: They are labor intensive, with rinsing and washing. You will use a lot more of these diapers because you cannot leave a baby in a wet diaper---and especially newborns will be going through them often. They do not wick moisture away from the baby (hence the changing more often). The rinsing and washing uses water---and I have heard some environmentalist who are opposed to cloth for this reason. I suppose that it depends on whether you are living in an area with water issues or not on this one. Although I consider myself an environmentalist also, I don't have a problem with water use, since the water can be reused after treating while a landfill will be there forever---or close to it.
It all comes down to what your comfort level is. Don't let yourself be forced into using one or the other diaper. Consider your time and what you can do.
And the most environmentally sound way would be to let the baby be naked all the time, if you ask me. I guess that wouldn't work well inside a house!