Hello @graz, only a personal test will bring clarity, because that is where the real facts are. Tests of others allow conclusions to be drawn conditionally.
I particularly like the S7 Edge with its 3,600 mAh battery, but my personal favorites are the S8 and S8+. With 3,500 mAh, the S8+ has only a slightly smaller battery than the S7 Edge.
However, the planned /e/ OS ROM with 9-Pie speaks for the S8 series, where against the S7 series currently only 8-Oero can be expected. The 9-Pie version does so much better than its predecessors, so that one can also speculate on a better energy management. But we won’t know until we’ve tried it out.