Do both - even if one only brings in 20% of the other that is still a worthy contribution!
Also I imagine if you are starting from scratch and promote heavily via Facebook then a Facebook store may be more effective but the only way to know is to test and then test some more and then some more!
Facebook is not good for building sales. It is more about branding and social interactions with potential customers/fans. I'd suggest LinkedIn for building b2b sales or your website for real sales instead.