I think cigarettes of French origin are stronger for sure. They tend to have a smaller filter and purer mix of tobacco. I don't think this applies to Bensons, Marlboro, etc.
American Marlboro lights (my preferred smoke) are very different from the UK/European ones. I wouldn't like to say stronger, but a very different flavour and are more aromatic. I don't really even like UK Marlboro now. I only smoke them if I run out of alternatives.
I have also smoked Marlboro lights from Malaysia, Thailand, Singapore, Hong Kong, Turkey, Spain (bit of an expert, eh) and they are very different again.
The Asian origin Marlboro are quite a bit stronger, the European ones tend to all taste the same, not as nice and packed full of chemicals.
I used to really like Fortuna (Spain) they don't 'seem' to have as many additives. They don't burn as well (a good sign) as major brands, have a great flavour and smell, and are cheap. They are strong though.
Hope this helps.