Some I believe are worse than others so it is something to keep an eye on.
My old school bus was fine, just usual hussle and bussle f.m has described, I now know it to be a problem. My neice taught in one of the school's it serves and it is one of the ones that they get most grief over. My friend's daughter, who travels on it, had big problems initially but her parents went direct to the parents (not always an option) and got it sorted.
I know in my current village one of the drop offs is such a problem that most of the children get off at the preceeding bus stop and walk the last bit. This is wrong and I can not accept that it is allowed to happen
. Thankfully my DS won't have to use this particular school bus, his gets back later. So longer bus journies do have their advantages.
Personally I would try to encourage the use of the school bus, be aware that bullying can sometimes happen and deal with it as and when it arises. I don't feel that one or two children should be able to make these buses no go areas and by reporting them only we can prevent that.