What are the easiest champs in each role?
I want to help my friend out who started playing.
Top:
Mid:
Jg:
ADC: Not sure since I never play this.
Support:
I want to help my friend out who started playing.
Top:
Mid:
Jg:
ADC: Not sure since I never play this.
Support:
No, noob teemos have a hard time vs. melee tops. Try Garen or Dr. Mundo top.
Mid Katarina is hard early because she can get poked out of lane. Annie is a good choice. Also try Lux.
Jg yes Warwick is easy and simple.
For ADC, try long range people like Cait or Ashe.
For support, try Janna or Morgana.
Top:

Jungle:

Mid:

ADC:

Support:

top:
mid
Jg:
adc
support:
I think Voli is the easiest champion in the game to play. He has an extremely straight forward kit and play pattern. He's good for learning basics like last hitting and trading.
Aside from that, I think:
Top: Garen is easy. Nautilus is also very straightforward and fun, though he can run into mana issues. Jg: WW, but I wouldn't recommend starting in the jg. Nunu is also easy to jungle with, but he's kind of terrible. Mid: Annie is good. lux is also good. She's a straightforward, safe skill shot champ. Good for learning the role.
I don't think you should send new players bot. It's a harder lane to learn IMO--if nothing else, there are twice as many champions down there, so there are twice as many things to worry about. Plus ADC has to CS and position well to do anything,
Yeah, make sure to tell him that you can get Dreadnight
, Unchained
, and Rocket Girl
by following them on Twitter, like them on Facebook, and subscribe to them on Youtube (i don't know if that's respectively or what rewards which champion). you get the champion for free as well.
Alistar is a little easier to execute now. They made his combo more reliable, and Alistar is pretty good... less so than he was nerfed recently (his ult).
Anything made by CertaintyT
Rammus Top Amumu Jungle Annie Mid Ashe ADC Soraka Supp
That depends, easiest to play mechanically? Easiest to win as overall? Easiest to play strategically? Easiest to carry with?
Soraka may be mechanically easy, but is very hard to strategize and can rarely carry without a lot of skill. As an example.
While Ekko takes more mechanical skill, but is easy to win as and easy to carry with.
This idea of 'easy' and 'hard' champions only applies to some.
New players shouldn't play Lee Sin or Azir for example. Unless you know, they are passionate for that character and don't mind losing at first.
Teemo is easy to play but almost impossible to carry with. New players shouldn't play Teemo.
My suggestions for a new player?

More importantly, whatever they find fun.
Top: Maokai, Kayle and Quinn Jungle: Kindred Mid: Ahri ADC: Tristana Support: Thresh or Soraka
Top:
Jungle:
Mid:
ADC:
Support:
These aren't necessarily the easiest of champions, but are my recommendations to all beginners to pick up, as they go more in depth into the game and allow you to learn more about the game sooner, rather than scraping by with the lowest of the low skill cap champions.
Braum's the true starter support. I don't see why people suggest all the squishy immobile supports that get bursted by everything.