I'd recommend having one of each type of Support.
1 Enchanter, 1 Mage, 1 Tank.
**Enchanter I'd recommend
or
. **
These two are the strongest Enchanter supports right now.
Nami is more focused on the early - mid game while Sona is your scaling Support.
If you can reach your Items on Sona and not get completely ruined, She is the best support in the mid - late game in terms of scaling.
**Mage I'd recommend
or
**
These two are just cancerous at all stages of the game.
Very oppressive to lane against and very oppressive in team fights.
These two can very easily make up for a bad ADC or bad mid laner in terms of damage output.
**Tank I'd recommend
or
**
Two very oppressive tanks to play against, both provide insane engage for their team and can peel very well.
They also get extremely tanky as the game goes on.