I saw a red post a while back declining Camille being the "definition of a diver" and it made me wonder what champions Riot considers the best example for each subclass.
(Others are welcome to share their opinions on this as well)
Vanguards: 
Wardens: New 
(fite me)
Juggernauts: 
Divers: 
Assassins: 
Skirmishers: 
or 
Burst mages: 
Battle mages: 
Artillery: 
Enchanters: 
Disruptors: 
Caster Marksmen: 
AA Marksmen: 
camille's aids though
darius for juggernauts
sion for vanguards
braum for wardens
Vi for divers
Zed for Assasins
Riven for skirmishers
Syndra for burst mages
Rumble for battle mages
Ziggs/Zerath for artillery mages
Orianna for disruptors
Marksman are a bit hard but lucian is the best caster one, Jhin for the poke ones, Varus for utility, and Jinx for hypercarries
for Vanguards.
for Wardens
for Divers.
for Skirmishers.
for Battle mages.
for Burst mages. (I feel she still somewhat lacks counterplay when she is strong though).
for Caster Marksman (When she isn't abusing items)
for Utility Marksman (Isn't she the only one?)
for Poke Marksman
/
for Hypercarry Marksman
Vanguard:
Warden: 
or
Juggernaut:
Diver: Tough call, but I think . However, this class is very likely to be reworked at Preseason 8, so we might get a more definitive answer.
Assassins:
Skirmishers: 
or 
, since we have basically killed Tank Ekko.
Burst Mages: Tough call, but I'll go with either 
or 
(for now...)
Battle Mages: 
or 
Artillery: 
Enchanters: 
or 
, frankly many of the champions here are pretty ok.
Disrupters:
Marksmen: 
for auto attacks, for caster.
Unique: 
I took these from this list that Riot made a few months ago. However please remember this is just my opinions as a single player and criticize my opinions as you all see fit.
A few people have specifically referred to Orianna as a poster child for Disruptors, and I have to disagree heavily. Orianna is pretty heavily defined by one aspect of her kit that is completely unrepresentative of Disruptors - front-loaded low-counterplay burst. A look at every other disruptor shows that their damage is backloaded and rife with counterplay, with Ori as the exception.
League's Design Director, Ghostcrawler, actually gave his own subjective answer to this question on his personal Tumblr blog a couple of months ago:
https://askghostcrawler.tumblr.com/post/155782009488/which-champions-do-you-feel-are-the-best
#“Which champions do you feel are the best representation of each subclass.”
WARNING: This is pretty subjective. You may feel differently.
Marksmen
Fighters
Mages
Slayers
Tanks
Controllers
Spoon Drawer
1/12/2017
I'll only speak for the subclass I have the most experience in.
is the quintessential juggernaut. The one gem that came out of the juggernaut shitshow update and has remained fairly intact up to today.
Shoutout to 
though for being the archetype of the class, a juggernaut before Riot even knew what juggernauts were.
The subclass names is just something they cooked up to justify some tankie dps champs.
for Diver
for Juggernaut
for Skirmisher
for Assassin
for Battle mage
for Burst mage
for Artillery mage
for Disruptors
for Enchanter
for Marksman (if we're talking about all marksmen in general, though they really are too varied to sit there and say one marksman defines what all marksmen should be).
