I recently hit 30, and I realise that I tend to /really/ suck at bot lanes and haven't bought a single champ that I can reliably use for them. For reference, main champions I use would be Noc/Annie/Panth/Warwick/Yi/Anivia/Teemo, though mainly the first three.
Tristana's also free if you....like their facebook page, I think? Not sure. That might not even still be a thing.
Ashe is also a decent ish choice, and she only costs 450 IP. She has a lot of utility, and her ult enables some fun plays. She is really easy to catch since her only means of escape is attacking with her slows. --- *waits until someone says something funny to quote*
ADC or support or both? Graves, MF, Ashe or Ezreal probably the easiest ADCs to learn. Basically if it isn't Vayne or Kog they are decently easy to learn. MF and Ashe are probably the easiest to learn because of the AOE imo, just sit back and blast people till they go away. If you play passive and methodical (as you should be when learning stuff you suck at) they will work out well in the beginning.
Graves has extra tankiness and a dash, so you can start learning to reposition yourself at a faster pace than the previous two. Then Ezreal takes mobility another step up and you can really practice on the fly positioning in conjunction with skill shots and autoattacks.
Support your go-to man is Taric. He's the most well balanced and all around effective for the role. You give the ADC armor by just being there, if your ADC is being attack you stun to peel people off him, and then heal him. When you are going in for a kill you stun, shred their armor and run around smacking people.
Sona and Soraka are also fairly straight forward, you just stand around healing and buffing while making sure not to die. You aren't as tanky as Taric so you are punished more for being risky, so just make sure to remember how easy you can die. If its really worth sacrificing your life for something do it, but do not feed kills unnecessarily.
I've tried Ashe when she's been free and... Iunno, I didn't like her too much. Her W just feels really... silly to me, since I don't see hitting more than 1 or 2 champs very likely, and her slows don't really appeal so much since I'm not really going to see myself chasing as ADC.
Might try Trist and Sivir out, though. Thanks for the suggestion.
I don't like ADC much either most of them just don't do it for me
the funner ones imo: Graves, Vayne, Twitch --- Hey what's going on in this thread http://i.imgur.com/9VkxI.gif My friend's YouTubes. She's got LP's and stuff. http://www.youtube.com/user/ratbirdchampion