"Needing a social media presence" could accurately be described as corporate peer pressure IMO. Facebook has successfully boiled the frog, so to speak, and as of late 2013 there are significant ongoing costs for maintaining a decent presence on the site. In my days as a marketing guy, my Facebook posts as of late 2014 had an average organic reach of about 1-2% to the people who had already liked our page... it was just outrageous. This post has some recent stats, which you could use to help make the case that being on Facebook nowadays is a needless marketing expense with little business value for newcomers/small businesses. The scary thing, as one commenter points out, is that those numbers are the average for all posts, paid or unpaid. If you plan on using Facebook for "free marketing" you are going to have a bad time. They may not want to hear that, though...
With that said, if you're working with people that really want you to have a social media presence, I'd recommend going with Twitter right now. It has a large userbase, including a lot of businesses, but my favorite part about it is that you really don't need to write any novels or take a lot of photos to maintain it. A lot of your tweets can be links to information that you consider relevant to clients/potential clients, like security bulletins. Then you can put your feed on your site with a widget - there are many WordPress plugins out there to help you accomplish that goal. Then there's a part of your site that can easily be updated with new stuff without having to write out whole blog posts.
It's also easier to use Twitter for direct calls to action with the Twitter Cards feature that came out a little while ago. For example, if you have a mailing list and tweet about it you can have a link to subscribe right on the tweet itself.
If you have staff active on Twitter, you can have the company follow them and retweet things they say that's relevant to what you do. Then you can have the "look we are real people" factor without having a discrete company directory. If I were into buzzwords I would describe these people as brand ambassadors but let's not go down that road...
Long story short, social media for businesses is most likely going to be seen as one of this decade's ridiculous tech fads in retrospect, but at the moment it is still going strong. In my opinion, Twitter has the best effort/expense to results ratio right now.
