I'm in agreement with Ben. It's totally subjective. Every poster who answers here will have a different take so this is actually more akin to a poll than a definitively answerable question.
My opinion- for loads under 30-35 pounds, I don't find much of a difference in comfort levels framed vs. framelss, provided the frameless pack has shoulder straps that distribute the load comfortable across my shoulders (wide, well padded) and there is some load transfer to my hips. I am probably at the upper fringe of frameless pack users when considering weight carried comfortably.
One note I will add that I see little discussion of when frameless packs are discussed is about physical conditioning. Strengthening your core muscles (abs, lower & upper back) goes a long way towards making pack carrying comfortable- that much more so with frameless packs. Work on those muscle groups and you will gain benefits much like those gained by carrying lighter gear. You will enjoy your hike more, think about your pack less, and be able to hike longer distances easier.