Original art vs newer is pretty broad-- things released simultaneously in US/UK for example can have different covers. And even your example of HP -- the original UK or original US? And classics, sheesh! What even is the original art for some of those?? I don't feel like this preference question is quite answerable, I sometimes see different artwork on formats for newer stuff!

I don't often read paper books anymore, I prefer a slightly larger font on kindle because I hate using reading glasses. But back before I was all eReader, I preferred Mass Market as those were easiest for me to handle and didn't have a weird texture I hate like some trade paperbacks. I hate dust covers sliding around and mostly lost those anyway for hardcovers.