There are different types of guttering (pvc, cast aluminium, cast iron) which comes in different shapes (deep flow, half round, squareline, ogee, miniline) which comes in different colours (brown, white, black, grey, cast iron imitation).
The gutter is designed to collect all of the roof's water, that is why it is important to have the gutter cleaned at least once a year. A full gutter will cause all sorts of problems such as overflowing, damaged joints, damaged brackets and damaged fascias.
Gutter guard is a mesh that stops any large debris such as leaves and moss from entering the gutter channel. It offers low cost and quick installation but does not offer complete protection.
Leaf guard is a step up from gutter guard as it offers a stronger and thicker mesh but at a slightly higher price, it too is a quick installation but does not offer 100% protection.
The gutter hedgehog is a foam spiked roll that lays in the gutter stopping any debris entering. It is probably the most common protection used as it comes at a reasonable price and offers a very good protection.
Gutter foam is a sponge foam extrusion that allows water to enter but stops any silt, moss, twigs and leaves entering. It comes at a higher cost but is probably the best gutter protection solution available.
The snow guard will prevent snow from falling down and prevent damage to the gutters. It comes at a reasonable price and is excellent in doing it's job.