Who is best suited to handle a company's social media marketing and execution?

I believe that in-house Social Media is preferred if there is a team/ person that has the passion and awareness of keeping the company's image, the responsibility to deliver the right and great reputation, along with the related experience or knowledge.

Outsourcing social media is risky.
Can someone outside of your office really understand your brand? How can they possibly create content without fully understanding your voice and values? Even though I am a social media consultant, my opinion is that every business does social media in-house if they have the knowledge and financial/labor resources to do so.

An internal online marketing specialist who is hired as a dedicated resource to live and breathe the company's social personality.
This person ideally would have at least 2-3 years of online experience handling everything from creating facebook, twitter and pintrest pages at a minimum, is adpet at creating and optimising ads, understands the tricks of conversion and understands the intricacies in creating an integrated online marketing mix.
Experience with blogs and affiliates is also key.
This person should be an expert on the brand personality and equity and should be a seasoned marketeer who understands the importance of awareness, conversion and loyalty tricks of online and offline.
The problem with outsourcing to an agency is you never get the priority and the time you need and the agency just "executes" versus "manages" the brand equity.

Great discussion going on! I think the decision here is primarily a function of what you need to achieve.
If "social" is only meant as a PR / branding platform then outsource, irrespective of your size and scale.
But if it's integral to your strategic business efforts, then you need to have some in-house expertise to achieve (and measure) genuine publicity and real engagement, as no one better than you can understand you.

I tend to disagree with the view that agency’s are confined to be executioners! It the relationship with the communication partners is based on a collaborative partnership – then you have a partner that is an extension of your marketing arm – that lives, breaths and share’s the same passion.
If they are perceived to be errand boys - then that’s what they will be.
If the dogma of the social platform is about a collaborative approach and dialogue – then we find ourselves at a stalemate right at the first hurdle itself.
That said, while the realm of social media and whose responsibility does it fall in – is hotly being debated.
I believe this is entirely depends on the strategic vision and discourse of the corporation.
My question is can corporations afford to be myopic and turn a blind eye to the kind of noise taking place on the SM channels? and can a corporation afford to deviate from its core competency and bring in the required clout – in terms of creative acumen, info-structure, intelligence and resources… to handle this on their own? Wouldn’t an communication partner with the required domain expertise and resources at hand – provide insight through cross pollinated learning’s for better competitive advantage.

Marketing team should oversee the social media.

Ofcourse inside a company with a dedicated resource who should be perfect in Social Media Strategies, Internet Marketing, how to market their products, must be clarified with Branding concept with specialization to Social Media research.
Have a Nice Day.
Syed Waqas Saghir Internet Marketing Expert.
http://www.cointelligence.co/

I think Social media is the "Swiss Army Knife" of PR.
Therefore, I am assuming a PR professional or a PR agency is best suited to handle social media activities.

I think the best person to handle social media marketing and execution is a person who thinks outside the square where he/she lives in i.e.
A Creative and Innovative Person.

I have always been an agency guy but I know both sides of the coin. The client side always has the internal knowledge but the real expertise always lies with the agency guys. So I would vote that these responsibilities should go to a good agency who can collaborate and connect with the client's objectives in a smooth manner and execute the same flawlessly.

The best results come from adopting an integrated approach to social media management.
Appointing internal resource for community management is definitely more cost effective over the long term.
However, agencies can add significant expertise and creative brain power when it comes to tactical campaigns.
In any case, any social media program needs to be anchored by clear strategic direction; something which is best served by the client.