LinkedIn is the largest, over 25 million, and best business network. It's becoming more of a business "social" network, now; and I belive it would be much larger now if it had developed more of its "social" aspects sooner.
If you're in business, you gotta be on LinkedIn. Here's my Profile below. The link that's circled in this graphic shows where you need to click on my Profile to connect directly with me and my connections.
