"snort of laughter" means the laughter with a snort,which sound showing the contempt,ridicule in one's credulity/difference/appearance/odd/...etc.
"laugh (at)" means "make fun of sb/st,scorn by laughing with the sounds out"
"giggle" means "an amusing person/thing,joking" or "laugh in half suppressed spasms without the sounds out loud "
These are some ways to laugh,so they're possitive or negative depends on the context,how to express(maybe a snort of laughter is just for fun,for example),...etc.