Superior option for gutters/downspouts?
Hands down, Stainless Steel. The hardest thing to dent out of all the choices, it has a good deal of spring where nothing else does. It won't turn ugly nor ever need paint &amp; comes in a number of wall thicknesses, get as thick as you're willing to afford. All of the same profile choices are available, something with a face profile will dramatically increase the durability. SS will hold up to ladders &amp; everything else the best.

Since you've noticed an overflow or possibly a Run-over issue with your current gutters, then definitely go up another size...an inch more in both height &amp; width. Also, make sure your current gutters aren't more than an inch below the roofing edge, &amp; that your roofing edge is no further than halfway across the gutter width. These would be the cause of Run-over. Don't skimp on screws, hangers or downspouts either. You'll never ever have to replace a single thing.