I am very content with my Sona whom I play with my AP carry runes (me am very lazy and prefer to buy champs than rune pages). She can inflict serious damage during early game with her Power Accord / Q combo. Furthermore, she basically has 7 skills.
- Free 20% Exhaust no AS debuff, but total damage output (Power Accord W)
- 40% Slow (Power Accord E)
- 2 nukes (Q and Power Accord Q)
- Movement speed buff
- armor and heal. While the Heal is not as powerful as Sorakas early on, especially with the lack of the armor buff, it is spammable and your HPS should be on par with Soraka's.
- AE stun
Especially in late game, when you have ridded yourself of mana consideration and have your full skillset available, you provide a shitton of utility to your team. If you do not play against a poke-intense double damage lane, prepare your enemies for a serious world of hurt, where one good combo by YOU takes out 1/3 - 1/4 of the opponent's life.