Sized to the roof draining into them
Capacity is a function of the roof above: its area, its pitch, and how many valleys concentrate the flow. A steep roof sheds the same storm faster, and an undersized run overflows at the inside corners first.
Often the fix is not bigger gutters but more downspouts — their count and placement move more water than the profile does.
Seamless, because joints are where gutters fail
Sectional gutters leak at their seams as the sealant ages; that is not a defect, it is what sealant does. Seamless runs are roll-formed to length on site, so the only joints left are corners and outlets.
Guards are a trade-off, not a magic lid
Guards do their best work against leaves. Shingle grit, seed pods and needles behave differently, and no cover ends maintenance — a good one turns a ladder job every season into an occasional rinse.
The honest question is what your trees drop. That picks the mesh and style better than any brochure.
The job is where the water lands
Gutters exist to move water away from the foundation. A downspout that empties beside the footing has moved the problem four feet.
Extensions, splash blocks and the grade they discharge onto are part of the design — wet basements and settled slabs are what failed drainage actually costs.