So many good champions.. It's gonna be really hard to pick just 5.
1. Vi - She was pretty much my first champion I ever played. And now, when I get put into games as her, I absolutely wreck people. The fact that she has 2 gap closers (Q and R), makes her even better IMO.
2. Darius - Kind of for the same reason as Tommy said. He has the AD of Master Yi, but can be built a lot tankier, which I like. That, and his passive is OP.
3. Kassadin - I don't even think I need to put a reason why Kassadin is on this list. He's mobile after 6, and he's just amazing.
4. Nami - Favorite support ever. It was really hard for me to get used to her bubble trap.. But once you get the hang of it, it's honestly almost as good as Blitzcrank's pull. That, and her ult is AoE.
5. Ezreal - Favorite ADC of all time. He's mobile and has a pretty good poke. And his Pulsefire Ezreal skin is pretty sick. Even though I'd never pay 25+ for a skin