Adding them to your page with no applicable content on the social networks provides no value. Like a ferrari without gas.
Before you work through the exercise ask yourself, are your customers or clients going to really utilize them on your site. Are they going to click on them? I see so many companies that put them in a high profile position and they get no activity. WASTE OF VALUABLE SPACE. If they aren' being used on your site but they do create alot of online activity from the social network,s get them connected to the home page in a lower profile position (footer) so you get the link juice value but you don't take up valuable space....
Doesn't matter where the buttons are on your page for SEO.
Add whatever social buttons you have that have activity and fit your customers, clients or vendors profiles....on the business to business side, our linked in activity has been very valuable. On our consumer side, facebook and twitter have been very valuable.
Home page pointing always makes the most sense for general seo. But if you have a special offer or something specific that you are trying to generate value or action, then move them to a specific URL landing page to optimize that value or action.
Hope this helps....cheers.