Thorns, you should probably just save up for another purchase, a crappy Yi recolor is definitely not worth your money. Buy Chosen Master Yi if you must get a Yi skin.
Sona used to be ridiculously OP until Riot nerfed her a lot, now she needs to get fed to be relevant. Still, a multi-target stun is always useful.
Anyways, my favorite champ is Udyr, as Thorns probably knows. I play him a lot in both ranked and casual games. In ranked games, I'm a tank that dies a lot, gets lots of assists, and does his duty as a jungler. In casual games, I roll out DPS builds, get fed, and carry my team.
There are really huge differences between experienced ranked players and players who only have around 200 games, from looking at our enemies as I play with Thorns.
For example, everyone knows how to build a champion. But the newer players don't know to pull back in the lane at 4 minutes, because that's when a jungler finishes his initial path to Level 4. They don't know about getting sight wards or using them properly. They don't know that dragon is worth 3 kills, and that once your team takes an advantage in a teamfight, you should immediately force a dragon. They don't know that First Mid Tower is the most important tower in the game, since it grants the most map control. Once it falls, you need to do your best to take down the enemy's mid tower.
There's a lot of things that go beyond simply learning to build and play your champion, and that is the beauty of LoL.