The tournament meta is different from the solo queue meta. Pub-stomp champions see much more success in solo queue where as they tend to be a lot weaker in a tournament environment. Don't see solo queue as the end all be all, solo queue means literally nothing in the grand scheme of things. (Don't even get me started on "normal") Your best bet to develop your skills (after learning mechanics and basic play) is to form a team and compete/scrim as often as possible. The main thing to look at from tournaments are the lane match-ups, counter picks, and the different ways that characters are built and used. Note what champions are doing well and then expect to see a large influx of those characters in the coming weeks.
tl;dr: Use solo queue to establish fundamental skills and then form a team to practice and actually develop those skills in a coordinated setting.
That being said, you can see success with any character if you play them well enough and your opponent screws up, that doesn't make the character any better though. It relies upon the "non-perfect" mechanics of your opponents.
I just give opinions on champions assuming that both players are on equal footing and playing their characters perfectly. Example: 9 times out of 10 karthus will lose to Ahri in lane (This can be further distorted by jungler variance and the other lanes)
Trying to tell someone what's good at every elo level is pointless. Just play a relatively good champion so much that you master them and are able to carry yourself to at least Gold. Anything below that is pretty meaningless as in that meta champion success is grossly scewed because of player error, not because of champion matchups.
Example: Lee Sin/Kassadin/Morgana/Shaco/Shen/Etc.. Almost always being banned at lower elo because they punish you for screwing up, they punish you hard.
Good champions to carry yourself with:
Top lane: Riven, Lee sin, Irelia
Mid lane: Ryze, Cassiopia, Karthus
AD: Graves, Corki, Vayne, Ashe
Support: Leona, Alistar, Janna
Jungler: Nocturne, Nautilus, Lee sin, Riven
Anything that can punish mistakes easily and snowball a game.
Also since I doubt this is getting dropped and I don't feel like going to bed, on the viability of ADs:
MF hasn't been used basically at all on a pro level since Dreamhack last year, which brings us almost to a full year. Not much to say on her, pretty obvious Riot has needed to do something for a long time. Chaox was trying her briefly several patches ago and TSM used her in some minor events but they wound up dropping her pretty quickly. Don't think anyone would argue she could use a little help, though I don't think she's as bad off as she's made out to be. Still enjoy the character a lot.
Chaox started playing her for a bit after M5 completely destroyed everyone with their own MF lane at and after IEM Hannover, he just wasn't very good with her. People even considered her the best AD carry (If not over powered) for a long time. Nunu + MF was seen almost everywhere.
The one AD I still think is a big problem is Urgot, just because I find his playstyle to be inherently uninteresting from a spectator perspective (zones more than almost any character in LoL, has a lockon mechanic so the room for counterplay is limited once he hits, swap is kind of exciting but tends to result in easy pickoffs that don't lead to fun teamfights, only really interesting to watch for the camera because of the chance of an enemy getting smeared before they can move which is interesting but not particularly fun), but crowds seem to disagree with me based on the reaction to some of the stuff Urgots do, I guess.
This tournament was pre-nerf Urgot, he got put in line, Ahri as well. The next patch notes (leaked and unofficial) looks to be nerfing Kog'maw a little bit by lowering his health and killing his ability to spam his ultimate.
The only one other than Sivir I think actually needs some help is Ezreal, since even though his midgame damage is pretty amazing you have to play twice as well with him to get the same damage as everyone else and he doesn't have massive utility or a really strong lategame to make up for it. Varus might fall under this too; his utility is a lot higher but it's a little disheartening to see how little use he's gotten from the pros since his release... I'd wager Draven will be seeing a lot more use at Dreamhack than Varus will already and that's not a good sign for the character.
Ezreal only needs a slight tweaking, some better scaling on his abilities. He's already played well enough as it is, he just falls off late game. Sivir is in a tight spot because of her range, they have to be careful when tweaking her because it's easy to throw her over the top while just as easily make her too underpowered. A slight buff to her damage should fix her up. Varus also needs a few more tweaks, increased scaling would increase his viability as well.
