Moving subsite to main site or subsite to single install?

Hi there,
Too much troubles with hosting the sub site of a customer. I'd like to give them the website which a sub site of my install.
What is the best option:
1. Duplicate my whole multisite platform on their hosting, and then clean it all - eliminating my other customers, sub sites, files and plugins? It will leave an empty main site and the site of the customer as a sub site.
2. From option1. move the sub site as the main site?
3. Export the sub site and install it as a single install on the new hosting?

What is the best option? Which is the easiest to achieve?
Critical installed plugins:
> Domain Mapping (which won't be necessary after migration for the main domain will be on the new server)

Please advise,