Whenever I look at a team composition, I always factor in a few things depending on what I expect to face. Do I want a relatively tanky team which can absorb burst damage? Do I want a bursty team which can wipe out squishy targets? Do I want physical or magic damage? AOE or concentrated? My suggestion would be to find the best of all of them.
A tank with strong initiation and survive-ability? Possibly Shen, Malphite, Shyvana, or Trundle.
A jungle with good brawling potential and lane pressure? Perhaps Shyvana, Jax, Lee Sin, Irelia, or Udyr.
An APC with good AOE and burst? You could check out Ziggz, Malzahar, Orianna, Annie, or Lissandra.
An ADC with consistent DPS, an escape, and concentrated damage? Caitlyn, Lucian, Ezreal, Jinx, or Corki.
A support who will help to keep the team alive and secure kills? Look for Sona, Karma, Janna, Nami, Leona, Thresh, Annie, Soraka, or Alistar.
These aren't all of them. But they are reliable champions who fit into their roles nicely. One of my own personal favorites would have to be:
Shen top, Pantheon Jungle, Orianna mid, Caitlyn ADC, and Karma support.
I hope this helps.