Best *battery* of current iPhone 6/7 options? (my iPhone 5 barely holds 3 hours with moderate use, not sure I can wait for an iPhone 8).

Had planned on holding out until the next iPhone 8 series came out, presumably later this year (yes? no?). But my old iPhone 5 battery is really going south fast in the last 6 months. Barely holds 3 hours with moderate use, and barely 90 minutes with really heavy use.

If I go ahead and upgrade now, which of the various iPhone 6 or 7 phones seems to have the very best battery??