I've only played the ones made by From Software. Here is my ranking so far:
1) Dark Souls
That's interesting. So you feel they're, for the most part, getting slightly worse each time? Is that because you played each one when it originally released? Or boss preferences? Or...?
I basically played Dark Souls 2 and 3 straight after one another, as if they hadn't been released years apart, so the improvements to for example the graphics and atmosphere were really stark to me.