Size and pitch
Standard five-inch gutter with too few downspouts overflows in a summer downpour, which is how water ends up behind fascia and against the wall. Six-inch gutter with adequately sized downspouts handles the rate this climate actually delivers.
Where the water goes
The single most important detail, and the most commonly ignored. A downspout dumping at the foundation saturates the soil beside the slab. Extend it, or pipe it away underground, so the discharge lands where it can drain.
What gutter installation is actually protecting
The wall and the foundation, not the roof. A gutter that overflows sends water behind the fascia and down the face of the wall, and a downspout that discharges at the slab saturates the soil beside it. Both of those are more expensive than the gutter by an order of magnitude, which is why sizing and discharge are worth more attention than the profile or the colour.
Guards
Worth it under oaks and pines, which is much of Central Florida. They reduce cleaning rather than eliminate it, and a guard that is sold as maintenance-free is being oversold.