As co-founder and CTO of my firm, I agree with many of the other responses: internal would be best, by far, assuming you like the existing team and have solid relationships therein.

With that said, shameless plug: if you are a senior-level IC who may be interested in getting a foot into management, we're hiring :)

Our company: bractlet.com

My email: brian at bractlet dot com

We're helping solve climate change through energy efficiency, and need talented folks to help us scale our systems and business to the next level.