last time I checked, penn engineering is ranked ahead of columbia's.
I'm in Penn's chemical and biomolecular engineering dept and considering medical school. Many premeds here are in bioengineering, which not only gives you an engineering degree but also has most med prereqs as major requirements. I'm not familiar with Columbia's program but i think it would be just as intense as penn, they are basically in the same tier. Both are also major biomedical research centres, so it would be easy for you to find projects that interests you at either place, if you happen to want to do biomedical research. For me, I would say the decision is primarily a matter of location. I personally would prefer new york to philadelphia.
engineering as premed is very doable. For me, all premed prereqs except 2 semesters of biology are already included in my major. All majors are difficult in one way or another. If you are truly interested in engineering, it should be no problem at all. It is only hard if you are doing it for ulterior motives.