I made this page before Dominion came out and now I decided it was time to edit it a bit now that we know more about this mode and have quite a bit of experiance playing it.
Defenders:
Primary Defender:
Someone who is able sit at one of their capture points no matter what. This person needs to be extremely decked out in whatever they need to survive any direct assult while ensuring that point stays in their possession. The best champions for the job are generally the ones who are super tanky and can heal themselves. Should also be taking advantage of nearby health shrines without moving too far away from the point. In desperate situations the Defender may need to become an impromptu Assaulter (which is not important enough for it's own category).
eg: Galio, Maokai, Shen
Summoners: Garrison, Heal Cleanse, Ghost, Exhaust
Counters: anyone who wanted a free capture
Countered by: Secondary Assaulter, Invasion Team, Pusher
Secondary Defender:
Unlike a Primary Defender, the Secondary isn't prepared to take a ton of damage. What they do is stand as far away from the capture point as they can while still ensuring it remains in their control with the use of long ranged harass. Also useful to have as back-up if the enemy brings in an Invasion Team. Generally won't be just sitting at the point since will most likely be unable to sustain themselves and will probably be needed elsewhere. Should be able to transition to Secondary Assaulter when need be.
eg: Kog'maw, Orianna, Nidalee
Summoners: Ghost, Exhaust, Flash, Cleanse, Garrison
Counters: Secondary Assaulter, Invasion Team
Countered by: Secondary Assaulter, Assassin, Pusher
Counter Pusher:
Typical defenders may have a rough time dealing with the amassed minions so the simplest counter is to push right back. Good choices to do this are champions that will be able to out-push the enemy pusher and quickly kill the opposing promoted minion. May have greater troubles against normal assaulters due to the need to build damage. Pretty much the same as a pusher but geared more to defend a point.
eg: Nunu, Heimerdinger, Swain
Summoners: Smite, Promote, Garrison, Exhaust, Ghost
Counters: Pusher
Countered by: Primary Assaulter, Invasion Team
Impromptu Defender:
After you assault or push a capture point and take it over you're not just going to leave it to allow the enemy team to quickly take it back, you're gonna need to defend it. Often however your Defender(s) will be busy on the other side of the map, you better hope your Assaulter/ Pusher is able to handle it, at least for a bit.
eg: Primary Assaulter, Pusher, Invader
Summoners: whatever you happen to have
Counters: anyone who wanted a free capture
Countered by: any reasonable attempt to take the capture point
Assaulters:
Primary Assaulter:
The person that wants to steal the point by killing or forcing out the Primary Defender. Needs to be able to tank the capture point turret while dishing out damage onto the Primary Defender. A great person to have the team's greater relic on. You could build pure damage and just use Garrison but since the Primary Assaulter will often need to become an Impromptu Defender this is not advised.
eg: Renekton, Poppy, Jarvan IV
Summoners: Garrison, Ghost, Ignite, Exhaust, Cleanse, Surge
Counters: anyone who just wanted to keep their capture point for free
Countered by: Secondary Defender, Support, Reinforcement
Secondary Assaulter:
Since often the Primary Assaulter won't have the damage to beat the Defender by themselves a Secondary Assulter building pure damage will be needed to slice through the Primary Defender and anyone else in the way. Should be able to trasition to Secondary Defender when need be.
eg: Caitlyn, Brand, Vayne
Summoners: Ignite, Ghost, Exhaust, Flash
Counters: Primary Defender, Secondary Defender, Support
Countered by: Secondary Defender, Assassin
Pusher:
Since capture points do not only have to be captured by a champion a Pusher is a great addition to a team. Often will start on the bottom of the map and will attempt to take the opposing capture point with an onslaut of minions.
eg: Sivir, Mordekaiser, Master Yi
Summoners: Promote (must), Exhaust, Ghost, Garrison, Smite
Counters: Primary Defender, Secondary Defender
Countered by: Assassin, Reinforcement, Counter Pusher
Invasion Team (Invader and Secondary Invader):
This two man team is great to have if you just can't kill the Primary Defender. While the Secondary Invader chanels for the capture the Invader distracts/ bullys the Primary Defender away from the vulnerable Secondary Invader long enough to ensure capture, the Invader must have good cc and/or an ability that will physically move the Primary Defender away from the capture point. This is a possible strategy but for most games the thing you'll want is to just pour damage on whoever is in the way to just force them off the point.
The Secondary Invader can be pretty much any champ with any summoner spells so it is a great time to have another role do this
eg: Sweeper, Support, Reinforcement
The Invader however can't be anyone.
eg: Blitzcrank, Janna, Leona
Summoners: Exhaust, Ghost, Flash, Cleanse
Counters: Primary Defender, Counter Pusher
Countered by: Secondary Defender, Assassin, Support, Reinforcement
Roamers:
Assassin:
High burst champion who's role is to kill anyone who is needed to be killed. (Excellent for catching over-extended Pushers, off-track Supports, greater relic hunters, etc.) A must have for peeling off pesky Secondary Defenders.
eg: Leblanc, Talon, Akali
Summoners: Ignite, Exhaust, Ghost, Flash, Cleanse
Counters: almost everyone
Countered by: Assassin, Reinforcement
Sweeper:
Someone who is always ready to "ninja" an enemy capture point when the opportunity arises. To ninja: the action of taking over one of an opponents unguarded capture points without them being able to respond in time. If they do send someone to defend, the Sweeper has the ability to either despose of or escape the said Defender.
eg: Wukong, Shaco, Twitch
Summoners: Ghost, Flash, Exhaust, Cleanse
Counters: anyone they can get to waste time chasing them/ waiting for them
Countered by: Assassin, Reinforcement
Support (Roaming Support):
Depending on the situation help may be needed for defending a point and/or staging an assult. The Support must be where it is needed. Generally not a desirable choice for most teams but for some situations it can work.
eg: Karma, Soraka, Sona
Summoners: Ghost, Heal, Exhaust, Garrison, Clarity
Counters: Primary Assaulter, Invasion Team
Countered by: Secondary Assaulter, Assassin
Reinforcement:
Fast moving and ready to assist any Defender or Assulter. If the Assulter doesn't have the greater relic this guy does. Also has to be on a constant lookout for pesky Sweepers. Pretty much this guy goes wherever there is need.
eg: Rammus, Kennen, Skarner
Summoners: Ghost
Counters: Primary Assaulter, Invasion Team, Assassin Sweeper, Reinforcement, Pusher
Countered by: Assassin, Reinforcement
(On a side note I predict that almost everyone will be Roamers in solo queue, doesn't matter if their champion is any good at it or not or if their team needs them to be where they're going, they will do it.)
^So often chaos.
Teemo!!!:
There was a request to make Teemo his own catagory so here it is! Place shrooms everywhere!!! Teemo = Shrooms, Shrooms = Control, Control = More Capturing and Holding, More Capturing and Holding = WIN; therefore Teemo = WIN. That is all.
*Thanks to Fluffdelgato for the addition of the "Sweeper"