Well.... welcome back i guess \o/ and for your question:
Windwalkers are a melee physical attack class type which usually uses evasion to avoid attacks and plays as a debuffer role, uses daggers
Snipers are a range physical attack class type which have long range and unleash high damage, uses gun

Assassins are almost the same as windwalker, uses dagger, evasion and physical damage
Sharpshooters are almost the same as Snipers, uses gun, long range and high output damage

now why i am telling you this, you first need to know who are they and what they can do, i cant really show you the differences between windwalker and snipers much cuz all is different, but i can show you the differences between wind walker and assassin or sniper and sharpshooter (maybe other people can explain further xD)

so the big difference between assassin and windwalker is that windwalkers have an unique skill called hide, it makes you stealth from the enemy vision and can set traps to kill them, while assassins are more depend on their debuffs to kill their enemy (its actually a very short description about them but its in general ^^)

now about sharpshooters and snipers, sharpshooters are similar to windwalkers a bit, setting traps from very high range(in fact they have the highest range in game) while snipers are have more mobility and highter damage than sharpshooters (again short description xD)

hope that helped a bit, i am sure there are some more people who have played those classes and can tell you more about them, hope you will have a wonderful gameplay here o/

Welcome back to Iris~

Ash's post is pretty much the jist of the classes really.

Sharpshooter are more support classes to their parties. Good with Crowd Control~
Sins in PvE are debuffers; very impt in a party. And in PvP theyre pretty strong as well
WW are debuffers as well, though seems like theyre better for PvP than PvE. Crowd controllers
Snipers are power houses with a bunch of stuns. Seem more solo-oriented than a sharpshooter

Theres no class that better than the other really; it just depends on your play style lol and vanity HAHAHAH Personally i like how hybrids look when its mail classes

Thank you both very much for your welcome and info! This helps me a lot!