Facebook and Twitter are both massive in terms of reach, so surely both are worth a shot. Here's some stats:

- Facebook has 350 million active users globally and they claim 50% log on daily and more than 700,000 local businesses have business pages on Facebook.
- Twitter has 75 million user accounts.
- LinkedIn has 11 milllion users across Europe.

You have to take these reported stats with a pinch of salt somewhat, but the scale is surely an opportunity, whatever business you're in.