i would say taric or soraka, since i'm a support main. with taric, you max W, you stun when your adc needs it for peel, not for a catch and everything works out fairly well. with soraka, you need fairly good positioning so you don't die, and if you do die, it's because they used a lot just to get to you.
for support, make sure you build for the team, not sure you. it does more than it seems.
for other roles;
adc: ashe isn't too hard to play, spam W to harass in lane, use ult to peel, not for a pick unless someone is already locked down and you are sure you can get something from it.
for top lane: garen is ban a lot right now so i'm going to dis-clude him. nasus is good if you can stack, game goes long enough and you build defence. GP is good, but hard to play really well. trundle is ok also. i would say cho makes for a forgiving top laner.
noct for assassin. he's the easiest to catch people out on.
for mages, it really depends on your style of play.
if you want to hard carry bronze 5, you really need to master taking advantage of the other team's mistakes and using your lead. if you want easier games, i would just say protect the adc so they don't need to worry as much and so they can deal more damage.